Systems and methods for electrosurgery

ABSTRACT

Methods and apparatus for selectively applying electrical energy to a target location within a patient&#39;s body, particularly including tissue in the spine. In a method of the invention high frequency (RF) electrical energy is applied to one or more active electrodes on an electrosurgical probe in the presence of an electrically conductive fluid to remove, contract or otherwise modify the structure of tissue targeted for treatment. In one aspect, a dura mater and spinal cord are insulated from the electrical energy by an insulator positioned on a non-active side of the probe. In another aspect, a plasma is aggressively formed in the electrically conductive fluid by delivering a conductive fluid to a distal end portion of the probe and aspirating the fluid from a location proximal of the return electrode. In another aspect, a distal end of an electrosurgical probe having at least one electrode on a biased, curved, bent, or steerable shaft is guided or steered to a target site within an intervertebral disc having a disc defect for treatment of tissue to be treated at the target site by the selective application of electrical energy thereto.

RELATED APPLICATIONS

[0001] This application claims priority from patent application Ser. No.09/676,194, entitled “Methods for Repairing Damaged IntervertebralDiscs”, filed Sep. 27, 2000 (Attorney Docket No. S-9) and ProvisionalPatent Application No. 60/204,206, filed May 12, 2000, which is acontinuation-in-part of U.S. patent application Ser. No. 09/026,851,entitled “Systems and Methods for Electrosurgical Spine Surgery,” filedFeb. 20, 1998, which is a continuation-in-part of U.S. patentapplication Ser. No. 08/690,159, entitled “Planar Ablation Probe andMethod for Electrosurgical Cutting and Ablation,” filed Jul. 18, 1996(Attorney Docket No. 16238-001610), the complete disclosure of which areincorporated herein by reference for all purposes. This application isalso a continuation-in-part of U.S. patent application Ser. No.09/316,472, entitled “Systems and Methods for Electrosurgical Treatmentof Intervertebral Discs,” filed May 21, 1999 which is acontinuation-in-part of U.S. patent application Ser. No. 09/295,687,entitled “Systems and Methods for Electrosurgical Treatment ofSubmucosal Tissue,” filed Apr. 21, 1999, U.S. patent application Ser.No. 09/054,323 entitled “Systems and Methods for ElectrosurgicalTreatment of Turbinates,” filed Apr. 2, 1998, and U.S. patentapplication Ser. No. 09/268,616, entitled “Systems and Methods forElectrosurgical Treatment of Sleep Obstructive Disorders,” filed Mar.15, 1999, the complete disclosures of which are incorporated byreference. This application also derives priority from U.S. patentapplication Ser. No. 08/942,580 entitled “Systems and Methods forElectrosurgical Tissue Contraction,” filed on Oct. 2, 1997 (AttorneyDocket No. 16238-001300) and U.S. patent application Ser. No. 08/990,374entitled “Systems and Methods for Endoscopic Sinus Surgery,” filed onDec. 15, 1997 (Attorney Docket No. E-3), the complete disclosures ofwhich are incorporated herein by reference for all purposes.

[0002] The present invention is related to commonly assigned co-pendingProvisional Patent Application Nos. 60/062,996 and 60/062,997,non-provisional U.S. patent application Ser. No. 08/970,239 entitled“Electrosurgical Systems and Methods for Treating the Spine,” filed Nov.14, 1997 (Attorney Docket No. 16238-001640), and Ser. No. 08/977,845entitled “Systems and Methods for Electrosurgical DermatologicalTreatment,” filed on Nov. 25, 1997 (Attorney Docket No. D-2), U.S.application Ser. No. 08/753,227, filed on Nov. 22, 1996 (Docket16238-002200), and PCT International Application, U.S. National PhaseSerial No. PCT/US94/05168, filed on May 10, 1994, now U.S. Pat. No.5,697,281, (Attorney Docket 16238-000440), which was acontinuation-in-part of application Ser. No. 08/059,681, filed on May10, 1993 (Attorney Docket 16238-000420), which was acontinuation-in-part of application Ser. No. 07/958,977, filed on Oct.9, 1992 (Attorney Docket 16238-000410) which was a continuation-in-partof application Ser. No. 07/817,575, filed on Jan. 7, 1992 (AttorneyDocket 16238-00040), the complete disclosures of which are incorporatedherein by reference for all purposes. The present invention is alsorelated to commonly assigned U.S. Pat. No. 5,683,366, filed Nov. 22,1995 (Attorney Docket 16238-000700), and U.S. Pat. No. 5,697,536, filedon Jun. 2, 1995 (Attorney Docket 16238-0006000), the completedisclosures of which are incorporated herein by reference for allpurposes.

BACKGROUND OF THE INVENTION

[0003] The present invention relates generally to the field ofelectrosurgery, and more particularly to surgical devices and methodswhich employ high frequency electrical energy to treat tissue in regionsof the spine. The present invention is particularly suited for thetreatment of herniated discs and other disorders of intervertebraldiscs. This invention also relates to treatment of an intervertebraldisc by guiding an electrosurgical probe to a target site within anintervertebral disc.

[0004] The major causes of persistent, often disabling, back pain aredisruption of the disc annulus, chronic inflammation of the disc (e.g.,herniation), or relative instability of the vertebral bodies surroundinga given disc, such as the instability that often occurs due to adegenerative disease. Spinal discs mainly function to cushion and tetherthe vertebrae, providing flexibility and stability to the patient'sspine. Spinal discs comprise a central hydrophilic cushion, the nucleuspulposus, surrounded by a multi-layered ligament, the annulus fibrosus.As discs degenerate, they lose their water content and height, bringingvertebrae closer together. This results in a weakening of the shockabsorption properties of the disc and a narrowing of the nerve openingsin the sides of the spine which may lead to pinching of the nerve root.This disc degeneration can cause back and leg pain. Weakness in theannulus fibrosus of degenerative discs, or disc injury, can allowfragments of the nucleus pulposus to migrate from within the disc intothe annulus fibrosus or the spinal canal. Displaced annulus fibrosus, orprotrusion of the nucleus pulposus, e.g., herniation, may impinge onspinal nerves or nerve roots. The mere proximity of the nucleus pulposusor a damaged annulus to a nerve can cause direct pressure against thenerve, resulting in pain and sensory and motor deficit.

[0005] Often, inflammation from disc herniation can be treatedsuccessfully by non-surgical means, such as rest, therapeutic exercise,oral anti-inflammatory medications or epidural injection ofcorticosteroids. In some cases, the disc tissue is irreparably damaged,thereby necessitating removal of a portion of the disc or the entiredisc to eliminate the source of inflammation and pressure. In moresevere cases, the adjacent vertebral bodies must be stabilized followingexcision of the disc material to avoid recurrence of the disabling backpain. One approach to stabilizing the vertebrae, termed spinal fusion,is to insert an interbody graft or implant into the space vacated by thedegenerative disc. In this procedure, a small amount of bone may begrafted and packed into the implants. This allows the bone to growthrough and around the implant, fusing the vertebral bodies andpreventing reoccurrence of the symptoms.

[0006] Until recently, spinal discectomy and fusion procedures resultedin major operations and traumatic dissection of muscle and bone removalor bone fusion. To overcome the disadvantages of traditional traumaticspine surgery, minimally invasive spine surgery was developed. Inendoscopic spinal procedures, the spinal canal is not violated andtherefore epidural bleeding with ensuring scarring is minimized orcompletely avoided. In addition, the risk of instability from ligamentand bone removal is generally lower in endoscopic procedures than withopen discectomy. Further, more rapid rehabilitation facilitates fasterrecovery and return to work.

[0007] Minimally invasive techniques for the treatment of spinaldiseases or disorders include chemonucleolysis, laser techniques andmechanical techniques. These procedures generally require the surgeon toform a passage or operating corridor from the external surface of thepatient to the spinal disc(s) for passage of surgical instruments,implants and the like. Typically, the formation of this operatingcorridor requires the removal of soft tissue, muscle or other types oftissue depending on the procedure (i.e., laparascopic, thoracoscopic,arthroscopic, back, etc.). This tissue is usually removed withmechanical instruments, such as pituitary rongeurs, curettes, graspers,cutters, drills, microdebriders and the like. Unfortunately, thesemechanical instruments greatly lengthen and increase the complexity ofthe procedure. In addition, these instruments might sever blood vesselswithin this tissue, usually causing profuse bleeding that obstructs thesurgeon's view of the target site.

[0008] Once the operating corridor is established, the nerve root isretracted and a portion or all of the disc is removed with mechanicalinstruments, such as a pituitary rongeur. In addition to the aboveproblems with mechanical instruments, there are serious concerns becausethese instruments are not precise, and it is often difficult, during theprocedure, to differentiate between the target disc tissue, and otherstructures within the spine, such as bone, cartilage, ligaments, nervesand non-target tissue. Thus, the surgeon must be extremely careful tominimize damage to the cartilage and bone within the spine, and to avoiddamaging nerves, such as the spinal nerves and the dura matersurrounding the spinal cord.

[0009] Lasers were initially considered ideal for spine surgery becauselasers ablate or vaporize tissue with heat, which also acts to cauterizeand seal the small blood vessels in the tissue. Unfortunately, lasersare both expensive and somewhat tedious to use in these procedures.Another disadvantage with lasers is the difficulty in judging the depthof tissue ablation. Since the surgeon generally points and shoots thelaser without contacting the tissue, he or she does not receive anytactile feedback to judge how deeply the laser is cutting. Becausehealthy tissue, bones, ligaments and spinal nerves often lie withinclose proximity of the spinal disc, it is essential to maintain aminimum depth of tissue damage, which cannot always be ensured with alaser.

[0010] Monopolar and bipolar radiofrequency devices have been used inlimited roles in spine surgery, such as to cauterize severed vessels toimprove visualization.

[0011] Monopolar devices, however, suffer from the disadvantage that theelectric current will flow through undefined paths in the patient'sbody, thereby increasing the risk of unwanted electrical stimulation toportions of the patient's body. In addition, since the defined paththrough the patient's body has a relatively high impedance (because ofthe large resistance or resistivity of the patient's body), largevoltage differences must typically be applied between the return andactive electrodes in order to generate a current suitable for ablationor cutting of the target tissue. This current, however, mayinadvertently flow along body paths having less impedance than thedefined electrical path, which will substantially increase the currentflowing through these paths, possibly causing damage to or destroyingsurrounding tissue or neighboring peripheral nerves.

[0012] There is a need for an apparatus or system including anelectrosurgical instrument, such as a catheter or probe, wherein theinstrument can be introduced into an intervertebral disc during anendoscopic procedure, and the distal portion of the instrument can beguided to a target site within the disc, wherein the target site can betreated with minimal or no damage to surrounding, non-target tissue. Theinstant invention provides such an electrosurgical system and methodsfor treating tissue by a cool ablation mechanism involving generation ofa plasma in the presence of an electrically conductive fluid andmolecular dissociation of tissue components, as is described in enablingdetail hereinbelow.

SUMMARY OF THE INVENTION

[0013] The present invention provides systems, apparatus and methods forselectively applying electrical energy to structures within a patient'sbody, such as tissue within or around the spine. The systems and methodsof the present invention are particularly useful for ablation,resection, aspiration, collagen shrinkage and/or hemostasis of tissueand other body structures in open and endoscopic spine surgery.

[0014] In one aspect of the invention, a method is provided for treatingdiscs within a patient's spine. Specifically, a method of the presentinvention comprises positioning at least one active electrode withinclose proximity of a disc in the spine (either endoscopically, orthrough an open procedure). The dura mater tissue that surrounds thespinal cord is insulated from the active electrode(s) and a highfrequency voltage is applied between the active electrode(s) and one ormore return electrodes to apply sufficient energy to the disc tissue toreduce the volume of the disc.

[0015] In one embodiment, the high frequency voltage is sufficient toablate at least a portion of the nucleus pulposus, either the extrudedportion outside the annulus or a portion or all of the nucleus pulposuswithin the annulus. In another embodiment, the active electrode isadvanced into the annulus and sufficient high frequency voltage isapplied to contract or shrink the collagen fibers within the nucleuspulposus. This causes the pulposus to shrink and withdraw from itsimpingement on the spinal nerve. In other embodiments, the presentinvention may be used to both ablate the extruded portion of the nucleuspulposus, and then to contract or shrink the inner disc material toallow repair of the annulus.

[0016] In a specific configuration, electrically conducting fluid, suchas isotonic saline, is directed to the target site between the targetdisc tissue and the active electrode. In monopolar embodiments, theconductive fluid need only be sufficient to surround the activeelectrode, and to provide a layer of fluid between the electrode and thetissue. In bipolar embodiments, the conductive fluid preferablygenerates a current flow path between the active electrode(s) and one ormore return electrodes.

[0017] In procedures requiring contraction of tissue, high frequencyvoltage is applied to the active electrode(s) to elevate the temperatureof collagen fibers within the tissue at the target site from bodytemperature (about 37° C.) to a tissue temperature in the range of about45° C. to 90° C., usually about 60° C. to 70° C., to substantiallyirreversibly contract these collagen fibers. In a preferred embodiment,an electrically conductive fluid is provided between the activeelectrode(s) and one or more return electrodes positioned on anelectrosurgical probe proximal to the active electrode(s) to provide acurrent flow path from the active electrode(s) away from the tissue tothe return electrode(s). The current flow path may be generated bydirecting an electrically conductive fluid along a fluid path past thereturn electrode and to the target site, or by locating a viscouselectrically conducting fluid, such as a gel, at the target site, andsubmersing the active electrode(s) and the return electrode(s) withinthe conductive gel. The collagen fibers may be heated either by passingthe electric current through the tissue to a selected depth before thecurrent returns to the return electrode(s) and/or by heating theelectrically conductive fluid and generating a jet or plume of heatedfluid which is directed towards the target tissue. In the latterembodiment, the electric current may not pass into the tissue at all. Inboth embodiments, the heated fluid and/or the electric current elevatesthe temperature of the collagen sufficiently to cause hydrothermalshrinkage of the collagen fibers.

[0018] In procedures requiring ablation of tissue, the tissue is removedby molecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel or saline) between the active electrode(s) and the tissue.Within the vaporized fluid an ionized plasma is formed, and chargedparticles (e.g., electrons) cause the molecular breakdown ordisintegration of several cell layers of the tissue. This moleculardissociation is accompanied by the volumetric removal of the tissue.This process can be precisely controlled to effect the volumetricremoval of tissue as thin as 10 microns to 150 microns with minimalheating of, or damage to, surrounding or underlying tissue structures. Amore complete description of this phenomenon is described in commonlyassigned U.S. Pat. No. 5,683,366, the complete disclosure of which isincorporated herein by reference.

[0019] In another aspect of the invention, the present invention isuseful for performing spinal surgery. The method comprises positioningan electrosurgical instrument in close proximity to an intervertebraldisc. An electrically conductive fluid is delivered toward a distal tipof the electrosurgical instrument. A high frequency electrical energy isapplied to the active electrode such that the conductive fluid completesa current flow path between the active electrode and a return electrode.The conductive fluid is aspirated through an aspiration lumen positionedproximal of the return electrode. Because the aspiration lumen ispositioned away from the fluid delivery lumen and proximal of the returnelectrode, a plasma can be aggressively created and the tissue can beablated or contracted more efficiently.

[0020] The tissue may be completely ablated in situ with the mechanismsdescribed above, or the tissue may be partially ablated and partiallyresected and aspirated from this operating corridor. In a preferredconfiguration, the probe will include one or more aspirationelectrode(s) at or near the distal opening of an aspiration lumen. Inthis embodiment, high frequency voltage is applied between theaspiration electrode(s) and one or more return electrodes (which can bethe same or different electrodes from the ones used to ablate tissue) topartially or completely ablate the tissue fragments as they areaspirated into the lumen, thereby preventing clogging of the lumen andexpediting the tissue removal process. In other configurations, theaspiration electrodes can be disposed within the aspiration lumen.

[0021] The present invention offers a number of advantages over currentmechanical and laser techniques for spine surgery. The ability toprecisely control the volumetric removal of tissue results in a field oftissue ablation or removal that is very defined, consistent andpredictable. The shallow depth of tissue heating also helps to minimizeor completely eliminate damage to healthy tissue structures, cartilage,bone and/or spinal nerves that are often adjacent the target tissue. Inaddition, small blood vessels within the tissue are simultaneouslycauterized and sealed as the tissue is removed to continuously maintainhemostasis during the procedure. This increases the surgeon's field ofview, and shortens the length of the procedure. Moreover, since thepresent invention allows for the use of electrically conductive fluid(contrary to prior art bipolar and monopolar electrosurgery techniques),isotonic saline may be used during the procedure. Saline is thepreferred medium for irrigation because it has the same concentration asthe body's fluids and, therefore, is not absorbed into the body as muchas certain other fluids.

[0022] Apparatus according to the present invention generally include anelectrosurgical probe or catheter having a shaft with proximal anddistal ends, one or more active electrode(s) at the distal end and oneor more connectors coupling the active electrode(s) to a source of highfrequency electrical energy. For endoscopic spine surgery, the shaftwill typically have a distal end portion sized to fit between adjacentvertebrae in the patient's spine. In some embodiments, the distal endportion can have an active side which has the active electrodes and aninsulated non-active side. In a specific use, the insulator can be usedto protect the dura mater (and spinal column) from iatrogenic injury.

[0023] Some embodiments of the electrosurgical probe can include a fluiddelivery element for delivering electrically conductive fluid to theactive electrode(s). The fluid delivery element may be located on theprobe, e.g., a fluid lumen or tube, or it may be part of a separateinstrument. In an exemplary embodiment, the lumen will extend through afluid tube exterior to the probe shaft that ends adjacent the distal tipof the shaft.

[0024] Alternatively, an electrically conducting gel or spray, such as asaline electrolyte or other conductive gel, may be applied to the targetsite. The electrically conductive fluid will preferably generate acurrent flow path between the active electrode(s) and one or more returnelectrodes. In an exemplary embodiment, the return electrode is locatedon the probe and spaced a sufficient distance from the activeelectrode(s) to substantially avoid or minimize current shortingtherebetween and to shield the return electrode from tissue at thetarget site.

[0025] In a specific configuration, the electrosurgical probe willinclude an electrically insulating electrode support member having atissue treatment surface at the distal end of the probe. One or moreactive electrode(s) are coupled to, or integral with, the electrodesupport member such that the active electrode(s) are spaced from thereturn electrode. In one embodiment, the probe includes an electrodearray having a plurality of electrically isolated active electrodesembedded in the electrode support member such that the active electrodesextend about 0.2 mm to about 10 mm from the tissue treatment surface ofthe electrode support member.

[0026] In other embodiments, the probe can include one or more lumensfor aspirating the electrically conductive fluid from the target area.In an exemplary embodiment, the lumen will extend along the exterior ofthe probe shaft and end proximal of the return electrode. In a specificconfiguration, the aspiration lumen and fluid delivery lumen both extendalong the exterior of the probe shaft in an annular configuration. Thefluid delivery lumen will extend to the distal tip of the shaft whilethe aspiration lumen will extend only to a point proximal of the returnelectrode.

[0027] In yet another aspect, the present invention provides a method oftreating an intervertebral disc having a nucleus pulposus and an annulusfibrosus. The method comprises advancing a distal end of anelectrosurgical instrument into the annulus fibrosus. The distal end ofthe electrosurgical instrument is moved, typically biased or steered, toa curved configuration that approximates a curvature of an inner surfaceof the annulus fibrosus. A high frequency voltage is delivered betweenan active electrode and a return electrode that are positioned on thedistal end of the electrosurgical instrument to treat the inner surfaceof the annulus fibrosus.

[0028] In yet another aspect, the present invention provides a method oftreating an intervertebral disc. The method comprises positioning adistal end of an electrosurgical probe within close proximity of anouter surface of the intervertebral disc. A high frequency voltage isdelivered between an active electrode and a return electrode. The highfrequency voltage is sufficient to create a channel in the disc tissue.The active electrode is then advanced through the channel created in theintervertebral disc. The distal end of the electrosurgical instrument ismoved to a curved configuration that approximates a curvature of aninner surface of the annulus fibrosus. A high frequency voltage isdelivered between the active electrode and the return electrode to treatthe inner surface of the annulus fibrosus.

[0029] In a further aspect, the present invention provides an apparatusfor treating an intervertebral disc. The apparatus comprises a steerabledistal end portion that is moveable to a curved configuration thatapproximates the curvature of the inner surface of an annulus fibrosus.At least one active electrode and a return electrode are positioned onthe distal end of the apparatus. A high frequency energy source isconfigured to create a voltage difference between the active electrodeand the return electrode. Preferably, the return electrode is positionedproximal of the active electrode so as to draw the electric current awayfrom the target tissue.

[0030] In another aspect, the present invention provides a method ofusing an electrosurgical system for treating a disorder of anintervertebral disc of a patient, wherein the electrosurgical systemincludes a power supply coupled to at least one active electrodedisposed on a shaft distal end of an electrosurgical probe. Such discdisorders include fragmentation and migration of the nucleus pulposusinto the annulus fibrosus, discogenic or axial pain, one or morefissures in the annulus fibrosus, or contained herniation (a protrusionof the nucleus pulposus which is contained within the annulus fibrosus)of the disc. The method includes inserting the shaft distal end withinthe intervertebral disc such that the active electrode is in thevicinity of the tissue targeted for treatment (fissure, containedherniation, etc.), and thereafter applying a high frequency voltagebetween the active electrode and a return electrode sufficient to ablatetarget tissue. In preferred embodiments, the voltage generates a plasmain the vicinity of the target site and tissue at the target site isablated by the molecular dissociation of disc tissue components to formlow molecular weight ablation by-products, the latter being readilyaspirated from the target site or tissue being treated.

[0031] In one embodiment, the shaft may be guided by a combination ofaxial translation of the shaft and rotation of the shaft about itslongitudinal axis. In one aspect of the invention, the shaft has apre-defined curvature, both before and after the shaft has been guidedto the vicinity of the contained herniation. The pre-defined curvaturemay include a first and a second curve in the shaft, the second curvebeing proximal to the first curve.

[0032] In another aspect of the invention, the shaft may lack apre-defined curvature, and may be bent to a suitable conformation priorto a particular surgical procedure. In yet another aspect of theinvention, the shaft may lack a pre-defined curvature, and the shaftdistal end may be steered during a surgical procedure so as to adopt asuitable conformation, thereby allowing the shaft distal end to beguided to a target site within an intervertebral disc.

[0033] By applying a high frequency voltage between the active electrodeand the return electrode, disc tissue at the target site undergoesmolecular dissociation. In one embodiment, the active electrode includesan electrode head having an apical spike and a cusp, wherein theelectrode head is adapted for providing a high current density in thevicinity of the electrode head when a high frequency voltage is appliedbetween the active electrode and the return electrode. The method may beconveniently performed percutaneously, and one or more stages in thetreatment or procedure may be performed under fluoroscopy to allowvisualization of the shaft within the disc to be treated.

[0034] Further aspects, features, and advantages of the presentinvention will appear from the following description in which thepreferred embodiments have been set forth in detail in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a perspective view of an electrosurgical systemincorporating a power supply and an electrosurgical probe for tissueablation, resection, incision, contraction and for vessel hemostasisaccording to the present invention;

[0036]FIG. 2 is a side view of an electrosurgical probe according to thepresent invention;

[0037]FIG. 3 is a cross-sectional view of a distal portion of the probeof FIG. 2;

[0038]FIG. 4 is an end view of the probe of FIG. 2, illustrating anarray of active electrodes;

[0039]FIG. 5 is an exploded view of the electrical connections withinthe probe of FIG. 2;

[0040] FIGS. 6-9 are end views of alternative embodiments of the probeof FIG. 2, incorporating aspiration electrode(s);

[0041]FIG. 10 is a longitudinal sectional view of the distal portion ofan electrosurgical probe;

[0042] FIGS. 11A-11C illustrate an alternative embodiment incorporatinga mesh electrode for ablating aspirated tissue fragments;

[0043] FIGS. 12-15 illustrate a method of performing a microendoscopicdiscectomy according to the principles of the present invention;

[0044]FIG. 16 is a schematic view of the proximal portion of anotherelectrosurgical system for endoscopic spine surgery incorporating anelectrosurgical instrument according to the present invention;

[0045]FIG. 17 is an enlarged view of a distal portion of theelectrosurgical instrument of FIG. 16;

[0046]FIG. 18 illustrates a method of ablating a volume of tissue fromthe nucleus pulposus of a herniated disc with the electrosurgical systemof FIG. 16;

[0047]FIG. 19 illustrates a planar ablation probe for ablating tissue inconfined spaces within a patient's body according to the presentinvention;

[0048]FIG. 20 illustrates a distal portion of the planar ablation probeof FIG. 19;

[0049]FIG. 21A is a front sectional view of the planar ablation probe,illustrating an array of semi-cylindrical active electrodes;

[0050]FIG. 21B is a front sectional view of an alternative planarablation probe, illustrating an array of active electrodes havingopposite polarities;

[0051]FIG. 22 is a top, partial sectional, view of the working end ofthe planar ablation probe of FIG. 19;

[0052]FIG. 23 is a side cross-sectional view of the working end of theplanar ablation probe, illustrating the electrical connection with oneof the active electrodes of FIG. 22;

[0053]FIG. 24 is a side cross-sectional view of the proximal end of theplanar ablation probe, illustrating the electrical connection with apower source connector;

[0054]FIG. 25 is a schematic view illustrating the ablation of meniscustissue located close to articular cartilage between the tibia and femurof a patient with the ablation probe of FIG. 19;

[0055]FIG. 26 is an enlarged view of the distal portion of the planarablation probe, illustrating ablation or cutting of meniscus tissue;

[0056]FIG. 27 illustrates a method of ablating tissue with a planarablation probe incorporating a single active electrode;

[0057]FIG. 28 is a schematic view illustrating the ablation of softtissue from adjacent surfaces of the vertebrae with the planar ablationprobe of the present invention;

[0058]FIG. 29 is a perspective view of an alternative embodiment of theplanar ablation probe incorporating a ceramic support structure withconductive strips printed thereon;

[0059]FIG. 30 is a top partial cross-sectional view of the planarablation probe of FIG. 29;

[0060]FIG. 31 is an end view of the probe of FIG. 30;

[0061]FIGS. 32A and 32B illustrate an alternative cage aspirationelectrode for use with the electrosurgical probes shown in FIGS. 2-11;

[0062] FIGS. 33A-33C illustrate an alternative dome shaped aspirationelectrode for use with the electrosurgical probes of FIGS. 2-11;

[0063] FIGS. 34-36 illustrates another system and method of the presentinvention for percutaneously contracting collagen fibers within anintervertebral disc with a small, needle-sized instrument;

[0064]FIG. 37A illustrates a system having a curved distal tip and aninsulator for protecting adjacent tissue;

[0065]FIG. 37B is an end view of one embodiment of the system of FIG.37A;

[0066]FIG. 38 illustrates the probe of FIG. 37A being percutaneouslyintroduced into a target intervertebral disc;

[0067]FIG. 39 shows the shaft distal end of the system of FIG. 37A withthe shaft distal end located within an intervertebral disc;

[0068]FIG. 40 is an electrosurgical probe having a fluid delivery lumenand an aspiration lumen;

[0069]FIG. 41 is an end view of the electrosurgical probe of FIG. 40;

[0070]FIG. 42 illustrates a system having an aspiration lumen and afluid delivery lumen;

[0071] FIGS. 43A-43D illustrate four embodiments of electrosurgicalprobes specifically designed for treating spinal defects;

[0072]FIG. 44 illustrates an electrosurgical system having a dispersivereturn pad for monopolar and/or bipolar operations;

[0073]FIG. 45 illustrates an electrosurgical probe being inserted intoan intervertebral disc;

[0074]FIGS. 46A and 46B illustrate the distal tip of the electrosurgicalprobe moving along an inner surface of the annulus fibrosus;

[0075]FIG. 47A is a side view of an electrosurgical probe having acurved shaft;

[0076]FIG. 47B is a side view of the distal end portion of the curvedshaft of FIG. 47A, with the shaft distal end portion within anintroducer device;

[0077]FIG. 47C is a side view of the distal end portion of the curvedshaft of FIG. 47B in the absence of the introducer device;

[0078]FIG. 48A is a side view of the distal end portion of anelectrosurgical probe showing an active electrode having an apical spikeand an equatorial cusp;

[0079]FIG. 48B is a cross-sectional view of the distal end portion ofthe electrosurgical probe of FIG. 48A;

[0080]FIG. 49A shows the distal end portion of the shaft of anelectrosurgical probe extended distally from an introducer needle;

[0081]FIG. 49B illustrates the position of the active electrode inrelation to the inner wall of the introducer needle upon retraction ofthe active electrode within the introducer needle;

[0082]FIGS. 50A, 50B show a side view and an end view, respectively, ofa curved shaft of an electrosurgical probe, in relation to an introducerneedle;

[0083]FIG. 51A shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a plurality of depthmarkings;

[0084]FIG. 51B shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a mechanical stop;

[0085]FIG. 52A schematically represents a normal intervertebral disc inrelation to the spinal cord;

[0086]FIG. 52B schematically represents an intervertebral discexhibiting a protrusion of the nucleus pulposus and a concomitantdistortion of the annulus fibrosus;

[0087]FIG. 52C schematically represents an intervertebral discexhibiting a plurality of fissures within the annulus fibrosus and aconcomitant distortion of the annulus fibrosus;

[0088]FIG. 52D schematically represents an intervertebral discexhibiting fragmentation of the nucleus pulposus and a concomitantdistortion of the annulus fibrosus;

[0089]FIG. 53 schematically represents translation of a curved shaft ofan electrosurgical probe within the nucleus pulposus for treatment of anintervertebral disc;

[0090]FIG. 54 shows a shaft of an electrosurgical probe within anintervertebral disc, wherein the shaft distal end is targeted to aspecific site within the disc;

[0091]FIG. 55 schematically represents a series of steps involved in amethod of ablating disc tissue according to the present invention;

[0092]FIG. 56 schematically represents a series of steps involved in amethod of guiding an electrosurgical probe to a target site within anintervertebral disc for ablation of targeted disc tissue, according toanother embodiment of the invention;

[0093]FIG. 57 shows treatment of an intervertebral disc using anelectrosurgical probe and a separately introduced ancillary device,according to another embodiment of the invention;

[0094]FIG. 58 is a side view of an electrosurgical probe having atracking device;

[0095]FIG. 59A shows a steerable electrosurgical probe wherein the shaftof the probe assumes a substantially linear configuration;

[0096]FIG. 59B shows the steerable electrosurgical probe of FIG. 59A,wherein the shaft distal end of the probe adopts a bent configuration;

[0097]FIG. 60 shows a steerable electrosurgical probe and an ancillarydevice inserted within the nucleus pulposus of an intervertebral disc;

[0098]FIG. 61A shows the shaft distal end of an electrosurgical probepositioned within an introducer extension tube and within an introducerneedle;

[0099]FIG. 61B shows the shaft distal end of the probe of FIG. 61Aextending beyond the distal end of both the introducer extension tubeand the introducer needle, with the shaft distal end adopting a curvedconfiguration;

[0100]FIG. 62A shows the distal end of an introducer extension tubeadvanced to a first position within an intervertebral disc with theshaft distal end accessing a first region of disc tissue; and

[0101]FIG. 62B shows the distal end of the introducer extension tubeadvanced to a second position within an intervertebral disc with theshaft distal end accessing a second region of disc tissue.

DESCRIPTION OF SPECIFIC EMBODIMENTS

[0102] The present invention provides systems and methods forselectively applying electrical energy to a target location within or ona patient's body, particularly including tissue or other body structuresin the spine. These procedures include laminectomy/disketomy proceduresfor treating herniated disks, decompressive laminectomy for stenosis inthe lumbosacral and cervical spine, medial facetectomy, posteriorlumbosacral and cervical spine fusions, treatment of scoliosisassociated with vertebral disease, foraminotomies to remove the roof ofthe intervertebral foramina to relieve nerve root compression andcervical and lumbar diskectomies, shrinkage of vertebral support tissue,and the like. These procedures may be performed through open procedures,or using minimally invasive techniques, such as thoracoscopy,arthroscopy, laparascopy or the like.

[0103] In the present invention, high frequency (RF) electrical energyis applied to one or more active electrodes in the presence ofelectrically conductive fluid to remove and/or modify the structure oftissue structures. Depending on the specific procedure, the presentinvention may be used to: (1) volumetrically remove tissue, bone,ligament or cartilage (i.e., ablate or effect molecular dissociation ofthe body structure); (2) cut or resect tissue or other body structures;(3) shrink or contract collagen connective tissue; and/or (4) coagulatesevered blood vessels.

[0104] In some procedures, e.g., shrinkage of nucleus pulposus inherniated discs, it is desired to shrink or contract collagen connectivetissue at the target site. In these procedures, the RF energy heats thetissue directly by virtue of the electrical current flow therethrough,and/or indirectly through the exposure of the tissue to fluid heated byRF energy, to elevate the tissue temperature from normal bodytemperatures (e.g., 37° C.) to temperatures in the range of 45° C. to90° C., preferably in the range from about 60° C. to 70° C. Thermalshrinkage of collagen fibers occurs within a small temperature rangewhich, for mammalian collagen is in the range from 60° C. to 70° C.(Deak, G., et al., “The Thermal Shrinkage Process of Collagen Fibres asRevealed by Polarization Optical Analysis of Topooptical StainingReactions,” Acta Morphologica Acad. Sci. of Hungary, Vol. 15(2), pp195-208, 1967). Collagen fibers typically undergo thermal shrinkage inthe range of 60° C. to about 70° C. Previously reported research hasattributed thermal shrinkage of collagen to the cleaving of the internalstabilizing cross-linkages within the collagen matrix (Deak, ibid). Ithas also been reported that when the collagen temperature is increasedabove 70° C., the collagen matrix begins to relax again and theshrinkage effect is reversed resulting in no net shrinkage (Allain, J.C., et al., “Isometric Tensions Developed During the HydrothermalSwelling of Rat Skin,” Connective Tissue Research, Vol. 7, pp. 127-133,1980). Consequently, the controlled heating of tissue to a precise depthis critical to the achievement of therapeutic collagen shrinkage. A moredetailed description of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580, filed Oct. 2, 1997, entitled “Systemsand Methods for Electrosurgical Tissue Contraction,” (Attorney DocketNo. 16238-001300), previously incorporated herein by reference.

[0105] The preferred depth of heating to effect the shrinkage ofcollagen in the heated region (i.e., the depth to which the tissue iselevated to temperatures between 60° C. to 70° C.) generally depends on(1) the thickness of the tissue, (2) the location of nearby structures(e.g., nerves) that should not be exposed to damaging temperatures,and/or (3) the volume of contraction desired to relieve pressure on thespinal nerve. The depth of heating is usually in the range from 0 to 3.5mm. In the case of collagen within the nucleus pulposus, the depth ofheating is preferably in the range from about 0 to about 2.0 mm.

[0106] In another method of the present invention, the tissue structuresare volumetrically removed or ablated. In this procedure, a highfrequency voltage difference is applied between one or more activeelectrode(s) and one or more return electrodes to develop high electricfield intensities in the vicinity of the target tissue site. The highelectric field intensities lead to electric field induced molecularbreakdown of target tissue through molecular dissociation (rather thanthermal evaporation or carbonization). Applicant believes that thetissue structure is volumetrically removed through moleculardisintegration of larger organic molecules into smaller molecules and/oratoms, such as hydrogen, oxides of carbon, hydrocarbons and nitrogencompounds. This molecular disintegration completely removes the tissuestructure, as opposed to dehydrating the tissue material by the removalof liquid within the cells of the tissue and extracellular fluids, as istypically the case with electrosurgical desiccation and vaporization.

[0107] The high electric field intensities may be generated by applyinga high frequency voltage that is sufficient to vaporize an electricallyconductive fluid over at least a portion of the active electrode(s) inthe region between the distal tip of the active electrode(s) and thetarget tissue. The electrically conductive fluid may be a gas or liquid,such as isotonic saline, delivered to the target site, or a viscousfluid, such as a gel, that is located at the target site. In the latterembodiment, the active electrode(s) are submersed in the electricallyconductive gel during the surgical procedure. Since the vapor layer orvaporized region has a relatively high electrical impedance, itminimizes the current flow into the electrically conducting fluid. Thisionization, under optimal conditions, induces the discharge of energeticelectrons and photons from the vapor layer and to the surface of thetarget tissue. A more detailed description of this cold ablationphenomenon, termed Coblation®, can be found in commonly assigned U.S.Pat. No. 5,683,366 the complete disclosure of which is incorporatedherein by reference.

[0108] The present invention applies high frequency (RF) electricalenergy in an electrically conductive fluid environment to remove (i.e.,resect, cut or ablate) or contract a tissue structure, and to sealtransected vessels within the region of the target tissue. The presentinvention is particularly useful for sealing larger arterial vessels,e.g., having a diameter on the order of 1 mm or greater. In someembodiments, a high frequency power supply is provided having anablation mode, wherein a first voltage is applied to an active electrodesufficient to effect molecular dissociation or disintegration of thetissue, and a coagulation mode, wherein a second, lower voltage isapplied to an active electrode (either the same or a differentelectrode) sufficient to achieve hemostasis of severed vessels withinthe tissue. In other embodiments, an electrosurgical probe is providedhaving one or more coagulation electrode(s) configured for sealing asevered vessel, such as an arterial vessel, and one or more activeelectrodes configured for either contracting the collagen fibers withinthe tissue or removing (ablating) the tissue, e.g., by applyingsufficient energy to the tissue to effect molecular dissociation. In thelatter embodiments, the coagulation electrode(s) may be configured suchthat a single voltage can be applied to coagulate with the coagulationelectrode(s), and to ablate or contract with the active electrode(s). Inother embodiments, the power supply and electrosurgical probe areconfigured such that the coagulation electrode is used when the powersupply is in the coagulation mode (low voltage), and the activeelectrode(s) are used when the power supply is in the ablation mode(higher voltage).

[0109] In the method of the present invention, one or more activeelectrodes are brought into close proximity to tissue at a target site,and the power supply is activated in the ablation mode such thatsufficient voltage is applied between the active electrodes and thereturn electrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, some vesselswithin the tissue may be severed. Smaller vessels will be automaticallysealed with the system and method of the present invention. Largervessels, and those with a higher flow rate, such as arterial vessels,may not be automatically sealed in the ablation mode. In these cases,the severed vessels may be sealed by activating a control (e.g., a footpedal) to reduce the voltage of the power supply into the coagulationmode. In this mode, the active electrodes may be pressed against thesevered vessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent probe may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

[0110] The present invention is particularly useful for removing orablating tissue around nerves, such as spinal or cranial nerves, e.g.,the spinal cord and the surrounding dura mater. One of the significantdrawbacks with the prior art cutters, graspers, and lasers is that thesedevices do not differentiate between the target tissue and thesurrounding nerves or bone. Therefore, the surgeon must be extremelycareful during these procedures to avoid damage to the bone or nerveswithin and around the spinal cord. In the present invention, theCoblation® process for removing tissue results in extremely small depthsof collateral tissue damage as discussed above. This allows the surgeonto remove tissue close to a nerve without causing collateral damage tothe nerve fibers.

[0111] In addition to the generally precise nature of the novelmechanisms of the present invention, applicant has discovered anadditional method of ensuring that adjacent nerves are not damagedduring tissue removal. According to the present invention, systems andmethods are provided for distinguishing between the fatty tissueimmediately surrounding nerve fibers and the normal tissue that is to beremoved during the procedure. Peripheral nerves usually comprise aconnective tissue sheath, or epineurium, enclosing the bundles of nervefibers to protect these nerve fibers. The outer protective tissue sheathor epineurium typically comprises a fatty tissue (e.g., adipose tissue)having substantially different electrical properties than the normaltarget tissue, such as the disc and other surrounding tissue that are,for example, removed from the spine during spinal procedures. The systemof the present invention measures the electrical properties of thetissue at the tip of the probe with one or more active electrode(s).These electrical properties may include electrical conductivity at one,several or a range of frequencies (e.g., in the range from 1 kHz to 100MHz), dielectric constant, capacitance or combinations of these. In thisembodiment, an audible signal may be produced when the sensingelectrode(s) at the tip of the probe detects the fatty tissuesurrounding a nerve, or direct feedback control can be provided to onlysupply power to the active electrode(s) either individually or to thecomplete array of electrodes, if and when the tissue encountered at thetip or working end of the probe is normal (e.g., non-fatty) tissue basedon the measured electrical properties.

[0112] In one embodiment, the current limiting elements (discussed indetail below) are configured such that the active electrodes, will shutdown or turn off when the electrical impedance reaches a thresholdlevel. When this threshold level is set to the impedance of the fattytissue surrounding nerves, the active electrodes will shut off wheneverthey come in contact with, or in close proximity to, nerves. Meanwhile,the other active electrodes, which are in contact with or in closeproximity to target tissue, will continue to conduct electric current tothe return electrode. This selective ablation or removal of lowerimpedance tissue in combination with the Coblation® mechanism of thepresent invention allows the surgeon to precisely remove tissue aroundnerves or bone.

[0113] In addition to the above, applicant has discovered that theCoblation® mechanism of the present invention can be manipulated toablate or remove certain tissue structures, while having little effecton other tissue structures. As discussed above, the present inventionuses a technique of vaporizing electrically conductive fluid to form aplasma layer or pocket around the active electrode(s), and then inducingthe discharge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conductive liquid) becomes sufficiently low (i.e.,less than approximately 10²⁰ atoms/cm³ for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 eV to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

[0114] The energy evolved by the energetic electrons may be varied byadjusting a variety of factors, such as: the number of activeelectrodes; electrode size and spacing; electrode surface area;asperities and sharp edges on the electrode surfaces; electrodematerials; applied voltage and power; current limiting means, such asinductors; electrical conductivity of the fluid in contact with theelectrodes; density of the fluid; and other factors. Accordingly, thesefactors can be manipulated to control the energy level of the excitedelectrons. Since different tissue structures have different molecularbonds, the present invention can be configured to break the molecularbonds of certain tissue, while having too low an energy to break themolecular bonds of other tissue. For example, fatty tissue, (e.g.,adipose tissue) has double bonds that require a substantially higherenergy level than 4 eV to 5 eV to break (typically on the order of about8 eV). Accordingly, the present invention in its current configurationgenerally does not ablate or remove such fatty tissue. However, thepresent invention may be used to effectively ablate cells to release theinner fat content in a liquid form. Of course, factors may be changedsuch that these double bonds can be broken (e.g., increasing the voltageor changing the electrode configuration to increase the current densityat the electrode tips).

[0115] The electrosurgical probe or catheter will comprise a shaft or ahandpiece having a proximal end and a distal end which supports one ormore active electrode(s). The shaft or handpiece may assume a widevariety of configurations, with the primary purpose being tomechanically support the active electrode and permit the treatingphysician to manipulate the electrode from a proximal end of the shaft.The shaft may be rigid or flexible, with flexible shafts optionallybeing combined with a generally rigid external tube for mechanicalsupport. Flexible shafts may be combined with pull wires, shape memoryactuators, and other known mechanisms for effecting selective deflectionof the distal end of the shaft to facilitate positioning of theelectrode(s) or electrode array. The shaft will usually include aplurality of wires or other conductive elements running axiallytherethrough to permit connection of the electrode array to a connectorat the proximal end of the shaft.

[0116] For endoscopic procedures within the spine, the shaft will have asuitable diameter and length to allow the surgeon to reach the targetsite (e.g., a disc) by delivering the shaft through the thoracic cavity,the abdomen or the like. Thus, the shaft will usually have a length inthe range of about 5.0 cm to 30.0 cm, and a diameter in the range ofabout 0.2 mm to about 20 mm. Alternatively, the shaft may be delivereddirectly through the patient's back in a posterior approach, which wouldconsiderably reduce the required length of the shaft. In any of theseembodiments, the shaft may also be introduced through rigid or flexibleendoscopes. Specific shaft designs will be described in detail inconnection with the drawings hereinafter.

[0117] In one embodiment, the probe may comprise a long, thin needle(e.g., on the order of about 1 mm in diameter or less) that can bepercutaneously introduced through the patient's back directly into thespine (see FIGS. 34-36). The needle will include one or more activeelectrode(s) for applying electrical energy to tissues within the spine.The needle may include one or more return electrodes, or the returnelectrode may be positioned on the patient's back, as a dispersive pad.In either embodiment, sufficient electrical energy is applied throughthe needle to the active electrode(s) to either shrink the collagenfibers within the intervertebral disk, or to ablate tissue within thedisk.

[0118] The current flow path between the active electrode(s) and thereturn electrode(s) may be generated by submerging the tissue site in anelectrically conductive fluid (e.g., within a liquid or a viscous fluid,such as an electrically conductive gel) or by directing an electricallyconductive fluid along a fluid path to the target site (i.e., a liquid,such as isotonic saline, or a gas, such as argon). This latter method isparticularly effective in a dry environment (i.e., the tissue is notsubmerged in fluid) because the electrically conductive fluid provides asuitable current flow path from the active electrode to the returnelectrode. A more complete description of an exemplary method ofdirecting electrically conductive fluid between the active and returnelectrodes is described in U.S. Pat. No. 5,697,536, previouslyincorporated herein by reference.

[0119] The electrically conductive fluid should have a thresholdconductivity to provide a suitable conductive path between the returnelectrode(s) and the active electrode(s). The electrical conductivity ofthe fluid (in units of millisiemens per centimeter or mS/cm) willusually be greater than 0.2 mS/cm, preferably will be greater than 2mS/cm, and more preferably greater than 10 mS/cm. In an exemplaryembodiment, the electrically conductive fluid is isotonic saline, whichhas a conductivity of about 17 mS/cm. Alternatively, the fluid may be anelectrically conductive gel or spray, such as a saline electrolyte gel,a conductive ECG spray, an electrode conductivity gel, an ultrasoundtransmission or scanning gel, or the like. Suitable gels or sprays arecommercially available from Graham-Field, Inc of Hauppauge, N.Y.

[0120] In some procedures it may also be necessary to retrieve oraspirate the electrically conductive fluid after it has been directed tothe target site. In addition, it may be desirable to aspirate smallpieces of tissue that are not completely disintegrated by the highfrequency energy, or other fluids at the target site, such as blood,mucus, the gaseous products of ablation, etc. Accordingly, the system ofthe present invention will usually include a suction lumen in the probe,or on another instrument, for aspirating fluids from the target site. Inaddition, the invention may include one or more aspiration electrode(s)coupled to the distal end of the suction lumen for ablating, or at leastreducing the volume of, non-ablated tissue fragments that are aspiratedinto the lumen. The aspiration electrode(s) function mainly to inhibitclogging of the lumen that may otherwise occur as larger tissuefragments are drawn therein. The aspiration electrode(s) may bedifferent from the ablation active electrode(s), or the sameelectrode(s) may serve both functions. A more complete description ofprobes incorporating aspiration electrode(s) can be found in commonlyassigned, co-pending patent application Ser. No. 09/010,382 filed Jan.21, 1998, the complete disclosure of which is incorporated herein byreference.

[0121] The present invention may use a single active electrode or anelectrode array distributed over a contact surface of a probe. In thelatter embodiment, the electrode array usually includes a plurality ofindependently current-limited and/or power-controlled active electrodesto apply electrical energy selectively to the target tissue whilelimiting the unwanted application of electrical energy to thesurrounding tissue and environment resulting from power dissipation intosurrounding electrically conductive liquids, such as blood, normalsaline, electrically conductive gel and the like. The active electrodesmay be independently current-limited by isolating the electrodes fromeach other and connecting each electrode to a separate power source thatis isolated from the other active electrodes. Alternatively, the activeelectrodes may be connected to each other at either the proximal ordistal ends of the probe to form a single wire that couples to a powersource.

[0122] In some embodiments, the active electrode(s) have an activeportion or surface with surface geometries shaped to promote theelectric field intensity and associated current density along theleading edges of the electrodes. Suitable surface geometries may beobtained by creating electrode shapes that include preferential sharpedges, or by creating asperities or other surface roughness on theactive surface(s) of the electrodes. Electrode shapes according to thepresent invention can include the use of formed wire (e.g., by drawinground wire through a shaping die) to form electrodes with a variety ofcross-sectional shapes, such as square, rectangular, L or V shaped, orthe like. Electrode edges may also be created by removing a portion ofthe elongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

[0123] Additionally or alternatively, the active electrode surface(s)may be modified through chemical, electrochemical or abrasive methods tocreate a multiplicity of surface asperities on the electrode surface.These surface asperities will promote high electric field intensitiesbetween the active electrode surface(s) and the target tissue tofacilitate ablation or cutting of the tissue. For example, surfaceasperities may be created by etching the active electrodes with etchantshaving a pH less than 7.0 or by using a high velocity stream of abrasiveparticles (e.g., grit blasting) to create asperities on the surface ofan elongated electrode.

[0124] The active electrode(s) are typically mounted in or on anelectrically insulating electrode support that extends from theelectrosurgical probe. In some embodiments, the electrode supportcomprises a plurality of wafer layers bonded together, e.g., by a glassadhesive or the like, or a single wafer. The wafer layer(s) haveconductive strips printed thereon to form the active electrode(s) andthe return electrode(s). In one embodiment, the proximal end of thewafer layer(s) will have a number of holes extending from the conductorstrips to an exposed surface of the wafer layers for connection toelectrical conductor lead traces in the electrosurgical probe orhandpiece. The wafer layers preferably comprise a ceramic material, suchas alumina, and the electrode will preferably comprise a metallicmaterial, such as gold, copper, platinum, palladium, tungsten, silver orthe like. Suitable multilayer ceramic electrodes are commerciallyavailable from e.g., VisPro Corporation of Beaverton, Oreg.

[0125] In one configuration, each individual active electrode in theelectrode array is electrically insulated from all other activeelectrodes in the array within the probe and is connected to a powersource which is isolated from each of the other active electrodes in thearray or to circuitry which limits or interrupts current flow to theactive electrode when low resistivity material (e.g., blood,electrically conductive saline irrigant or electrically conductive gel)causes a lower impedance path between the return electrode and theindividual active electrode. The isolated power sources for eachindividual active electrode may be separate power supply circuits havinginternal impedance characteristics which limit power to the associatedactive electrode when a low impedance return path is encountered. By wayof example, the isolated power source may be a user-selectable constantcurrent source. In this embodiment, lower impedance paths willautomatically result in lower resistive heating levels since the heatingis proportional to the square of the operating current times theimpedance. Alternatively, a single power source may be connected to eachof the active electrodes through independently actuatable switches, orby independent current limiting elements, such as inductors, capacitors,resistors and/or combinations thereof. The current limiting elements maybe provided in the probe, connectors, cable, controller or along theconductive path from the controller to the distal tip of the probe.Alternatively, the resistance and/or capacitance may occur on thesurface of the active electrode(s) due to oxide layers which formselected active electrodes (e.g., titanium or a resistive coating on thesurface of metal, such as platinum).

[0126] The tip region of the probe may comprise many independent activeelectrodes designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual active electrode and thereturn electrode to a power source having independently controlled orcurrent limited channels. The return electrode(s) may comprise a singletubular member of conductive material proximal to the electrode array atthe tip which also serves as a conduit for the supply of theelectrically conductive fluid between the active and return electrodes.Alternatively, the probe may comprise an array of return electrodes atthe distal tip of the probe (together with the active electrodes) tomaintain the electric current at the tip. The application of highfrequency voltage between the return electrode(s) and the electrodearray results in the generation of high electric field intensities atthe distal tips of the active electrodes with conduction of highfrequency current from each individual active electrode to the returnelectrode. The current flow from each individual active electrode to thereturn electrode(s) is controlled by either active or passive means, ora combination thereof, to deliver electrical energy to the surroundingconductive fluid while minimizing energy delivery to surrounding(non-target) tissue.

[0127] The application of a high frequency voltage between the returnelectrode(s) and the active electrode(s) for appropriate time intervalseffects cutting, removing, ablating, shaping, contracting or otherwisemodifying the target tissue. The tissue volume over which energy isdissipated (i.e., a high current density exists) may be preciselycontrolled, for example, by the use of a multiplicity of small activeelectrodes whose effective diameters or principal dimensions range fromabout 5 mm to 0.01 mm, preferably from about 2 mm to 0.05 mm, and morepreferably from about 1 mm to 0.1 mm. Electrode areas for both circularand non-circular electrodes will have a contact area (per activeelectrode) below 25 mm², preferably being in the range from 0.0001 mm²to 1 mm², and more preferably from 0.005 mm² to 0.5 mm². Thecircumscribed area of the electrode array is in the range from 0.25 mm²to 200 mm², preferably from 0.5 mm² to 100 m², and will usually includeat least two isolated active electrodes, preferably at least five activeelectrodes, often greater than ten active electrodes and even fifty ormore active electrodes, disposed over the distal contact surfaces on theshaft. The use of small diameter active electrodes increases theelectric field intensity and reduces the extent or depth of tissueheating as a consequence of the divergence of current flux lines whichemanate from the exposed surface of each active electrode.

[0128] The area of the tissue treatment surface can vary widely, and thetissue treatment surface can assume a variety of geometries, withparticular areas and geometries being selected for specificapplications. Active electrode surfaces can have areas in the range from0.25 mm² to 75 mm², usually being from about 0.5 mm² to 40 mm². Thegeometries can be planar, concave, convex, hemispherical, conical,linear “in-line” array or virtually any other regular or irregularshape. Most commonly, the active electrode(s) or active electrode(s)will be formed at the distal tip of the electrosurgical probe shaft,frequently being planar, disk-shaped, or hemispherical surfaces for usein reshaping procedures or being linear arrays for use in cutting.Alternatively or additionally, the active electrode(s) may be formed onlateral surfaces of the electrosurgical probe shaft (e.g., in the mannerof a spatula), facilitating access to certain body structures inendoscopic procedures.

[0129] It should be clearly understood that the invention is not limitedto electrically isolated active electrodes, or even to a plurality ofactive electrodes. For example, the array of active electrodes may beconnected to a single lead that extends through the probe shaft to apower source of high frequency current. Alternatively, the probe mayincorporate a single electrode that extends directly through the probeshaft or is connected to a single lead that extends to the power source.The active electrode may have a ball shape (e.g., for tissuevaporization and desiccation), a twizzle shape (for vaporization andneedle-like cutting), a spring shape (for rapid tissue debulking anddesiccation), a twisted metal shape, an annular or solid tube shape orthe like. Alternatively, the electrode may comprise a plurality offilaments, a rigid or flexible brush electrode (for debulking a tumor,such as a fibroid, bladder tumor or a prostate adenoma), a side-effectbrush electrode on a lateral surface of the shaft, a coiled electrode orthe like. In one embodiment, the probe comprises a single activeelectrode that extends from an insulating member, e.g., ceramic, at thedistal end of the probe. The insulating member is preferably a tubularstructure that separates the active electrode from a tubular or annularreturn electrode positioned proximal to the insulating member and theactive electrode.

[0130] In some embodiments, the electrode support and the fluid outletmay be recessed from an outer surface of the probe or handpiece toconfine the electrically conductive fluid to the region immediatelysurrounding the electrode support. In addition, the shaft may be shapedso as to form a cavity around the electrode support and the fluidoutlet. This helps to assure that the electrically conductive fluid willremain in contact with the active electrode(s) and the returnelectrode(s) to maintain the conductive path therebetween. In addition,this will help to maintain a vapor or plasma layer between the activeelectrode(s) and the tissue at the treatment site throughout theprocedure, which reduces the thermal damage that might otherwise occurif the vapor layer were extinguished due to a lack of conductive fluid.Provision of the electrically conductive fluid around the target sitealso helps to maintain the tissue temperature at desired levels.

[0131] The voltage applied between the return electrode(s) and theelectrode array will be at high or radio frequency, typically betweenabout 5 kHz and 20 MHz, usually being between about 30 kHz and 2.5 MHz,preferably being between about 50 kHz and 500 kHz, more preferably lessthan 350 kHz, and most preferably between about 100 kHz and 200 kHz. TheRMS (root mean square) voltage applied will usually be in the range fromabout 5 volts to 1000 volts, preferably being in the range from about 10volts to 500 volts depending on the active electrode size, the operatingfrequency and the operation mode of the particular procedure or desiredeffect on the tissue (i.e., contraction, coagulation or ablation).Typically, the peak-to-peak voltage will be in the range of 10 volts to2000 volts, preferably in the range of 20 volts to 1200 volts and morepreferably in the range of about 40 volts to 800 volts (again, dependingon the electrode size, the operating frequency and the operation mode).

[0132] As discussed above, the voltage is usually delivered in a seriesof voltage pulses or alternating current of time varying voltageamplitude with a sufficiently high frequency (e.g., on the order of 5kHz to 20 MHz) such that the voltage is effectively applied continuously(as compared with e.g., lasers claiming small depths of necrosis, whichare generally pulsed about 10 Hz to 20 Hz). In addition, the duty cycle(i.e., cumulative time in any one-second interval that energy isapplied) is on the order of about 50% for the present invention, ascompared with pulsed lasers which typically have a duty cycle of about0.0001%.

[0133] The preferred power source of the present invention delivers ahigh frequency current selectable to generate average power levelsranging from several milliwatts to tens of watts per electrode,depending on the volume of target tissue being heated, and/or themaximum allowed temperature selected for the probe tip. The power sourceallows the user to select the voltage level according to the specificrequirements of a particular spine procedure, arthroscopic surgery,dermatological procedure, ophthalmic procedures, FESS procedure, opensurgery or other endoscopic surgery procedure. A description of asuitable power source can be found in U.S. Provisional PatentApplication No. 60/062,997 entitled “Systems and Methods forElectrosurgical Tissue and Fluid Coagulation,” filed Oct. 23, 1997(Attorney Docket No. 16238-007400), the complete disclosure of which isincorporated herein by reference.

[0134] The power source may be current limited or otherwise controlledso that undesired heating of the target tissue or surrounding(non-target) tissue does not occur. In a presently preferred embodimentof the present invention, current limiting inductors are placed inseries with each independent active electrode, where the inductance ofthe inductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously in copendingPCT application No. PCT/US94/05168, the complete disclosure of which isincorporated herein by reference. Additionally, current limitingresistors may be selected. Preferably, these resistors will have a largepositive temperature coefficient of resistance so that, as the currentlevel begins to rise for any individual active electrode in contact witha low resistance medium (e.g., saline irrigant or conductive gel), theresistance of the current limiting resistor increases significantly,thereby minimizing the power delivery from the active electrode into thelow resistance medium (e.g., saline irrigant, a conductive gel, ornatural body fluids such as blood).

[0135] Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the spine will now be described in detail.Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site, and a fluid source 21 for supplyingelectrically conductive fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site, particularly inendoscopic spine procedures. The endoscope may be integral with probe10, or it may be part of a separate instrument. The system 11 may alsoinclude a vacuum source (not shown) for coupling to a suction lumen ortube 211 (see FIG. 2) in the probe 10 for aspirating the target site.

[0136] As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of active electrodes 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the active electrodes 58 to power supply 28. The activeelectrodes 58 are electrically isolated from each other and each of theelectrodes 58 is connected to an active or passive control networkwithin power supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conductive fluid 50 tothe target site.

[0137] Power supply 28 has an operator controllable voltage leveladjustment 30 to change the applied voltage level, which is observableat a voltage level display 32. Power supply 28 also includes first,second and third foot pedals 37, 38, 39 and a cable 36 which isremovably coupled to power supply 28. The foot pedals 37, 38, 39 allowthe surgeon to remotely adjust the energy level applied to activeelectrodes 58. In an exemplary embodiment, first foot pedal 37 is usedto place the power supply into the “ablation” mode and second foot pedal38 places power supply 28 into the “coagulation” mode. The third footpedal 39 allows the user to adjust the voltage level within the“ablation” mode. In the ablation mode, a sufficient voltage is appliedto the active electrodes to establish the requisite conditions formolecular dissociation of the tissue, as described elsewhere herein. Asdiscussed above, the requisite voltage level for ablation will varydepending on the number, size, shape and spacing of the electrodes, thedistance to which the electrodes extend from the support member, etc.Once the surgeon places the power supply in the “ablation” mode, voltagelevel adjustment 30 or third foot pedal 39 may be used to adjust thevoltage level to adjust the degree or aggressiveness of the ablation.

[0138] Of course, it will be recognized that the voltage and modality ofthe power supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

[0139] In the coagulation mode, the power supply 28 applies a low enoughvoltage to the active electrodes (or the coagulation electrode) to avoidvaporization of the electrically conductive fluid and subsequentmolecular dissociation of the tissue. The surgeon may automaticallytoggle the power supply between the ablation and coagulation modes byalternatively stepping on foot pedals 37, 38, respectively. This allowsthe surgeon to quickly move between coagulation and ablation in situ,without having to remove his/her concentration from the surgical fieldor without having to request an assistant to switch the power supply. Byway of example, as the surgeon is sculpting or ablating soft tissue inthe ablation mode, the probe typically will simultaneously seal and/orcoagulate any small severed vessels within the tissue. However, largervessels, or vessels with high fluid pressures (e.g., arterial vessels)may not be sealed in the ablation mode. Accordingly, the surgeon cansimply step on foot pedal 38, automatically lowering the voltage levelbelow the threshold level for ablation, and apply sufficient pressureonto the severed vessel for a sufficient period of time to seal and/orcoagulate the vessel. After this is completed, the surgeon may quicklymove back into the ablation mode by stepping on foot pedal 37. Aspecific design of a suitable power supply for use with the presentinvention can be found in U.S. Provisional Patent Application No.60/062,997, entitled “Systems and Methods for Electrosurgical Tissue andFluid Coagulation,” filed Oct. 23, 1997 (Attorney Docket No.16238-007400), which is incorporated herein by reference.

[0140] FIGS. 2-5 illustrate an exemplary electrosurgical probe 20constructed according to the principles of the present invention. Asshown in FIG. 2, probe 20 generally includes an elongated shaft 100which may be flexible or rigid, a handle 204 coupled to the proximal endof shaft 100 and an electrode support member 102 coupled to the distalend of shaft 100. Shaft 100 preferably comprises a plastic material thatis easily molded into the shape shown in FIG. 2. In an alternativeembodiment (not shown), shaft 100 comprises an electrically conductingmaterial, usually metal, which is selected from the group comprisingtungsten, stainless steel alloys, platinum or its alloys, titanium orits alloys, molybdenum or its alloys, and nickel or its alloys. In thisembodiment, shaft 100 includes an electrically insulating jacket 108,which is typically formed as one or more electrically insulating sheathsor coatings, such as polytetrafluoroethylene, polyimide, and the like.The provision of electrically insulating jacket 108 over the shaftprevents direct electrical contact between these metal elements and anyadjacent body structure or the surgeon. Such direct electrical contactbetween a body structure (e.g., tendon) and an exposed electrode couldresult in unwanted heating of the structure at the point of contactcausing necrosis.

[0141] Handle 204 typically comprises a plastic material that is easilymolded into a suitable shape for handling by the surgeon. Handle 204defines an inner cavity (not shown) that houses the electricalconnections 250 (FIG. 5), and provides a suitable interface forconnection to an electrical connecting cable 22 (see FIG. 1). Electrodesupport member 102 extends from the distal end of shaft 100 (usuallyabout 1 mm to 20 mm), and provides support for a plurality ofelectrically isolated active electrodes 104 (see FIG. 4). As shown inFIG. 2, a fluid tube 233 extends through an opening in handle 204, andincludes a connector 235 for connection to a fluid supply source, forsupplying electrically conductive fluid to the target site. Fluid tube233 is coupled to a distal fluid tube 239 that extends along the outersurface of shaft 100 to an opening 237 at the distal end of the probe20, as discussed in detail below. Of course, the invention is notlimited to this configuration. For example, fluid tube 233 may extendthrough a single lumen (not shown) in shaft 100, or it may be coupled toa plurality of lumens (also not shown) that extend through shaft 100 toa plurality of openings at its distal end. Probe 20 may also include avalve 17 (FIG. 1) or equivalent structure for controlling the flow rateof the electrically conductive fluid to the target site.

[0142] As shown in FIGS. 3 and 4, electrode support member 102 has asubstantially planar tissue treatment surface 212 and comprises asuitable insulating material (e.g., ceramic or glass material, such asalumina, zirconia and the like) which could be formed at the time ofmanufacture in a flat, hemispherical or other shape according to therequirements of a particular procedure. The preferred support membermaterial is alumina, available from Kyocera Industrial CeramicsCorporation, Elkgrove, Ill., because of its high thermal conductivity,good electrically insulative properties, high flexural modulus,resistance to carbon tracking, biocompatibility, and high melting point.The support member 102 is adhesively joined to a tubular support member(not shown) that extends most or all of the distance between supportmember 102 and the proximal end of probe 20. The tubular memberpreferably comprises an electrically insulating material, such as anepoxy or silicone-based material.

[0143] In a preferred construction technique, active electrodes 104extend through pre-formed openings in the support member 102 so thatthey protrude above tissue treatment surface 212 by the desireddistance. The electrodes 104 are then bonded to the tissue treatmentsurface 212 of support member 102, typically by an inorganic sealingmaterial. The sealing material is selected to provide effectiveelectrical insulation, and good adhesion to both the alumina member 102and the platinum or titanium active electrodes 104. The sealing materialadditionally should have a compatible thermal expansion coefficient anda melting point well below that of platinum or titanium and alumina orzirconia, typically being a glass or glass ceramic.

[0144] In the embodiment shown in FIGS. 2-5, probe 20 includes a returnelectrode 112 for completing the current path between active electrodes104 and a high frequency power supply 28 (see FIG. 1). As shown, returnelectrode 112 preferably comprises an annular conductive band coupled tothe distal end of shaft 100 slightly proximal to tissue treatmentsurface 212 of electrode support member 102, typically about 0.5 mm to10 mm and more preferably about 1 mm to 10 mm proximal to surface 212.Return electrode 112 is coupled to a connector 258 (FIG. 5) that extendsto the proximal end of probe 10, where it is suitably connected to powersupply 28 (FIG. 1).

[0145] As shown in FIG. 2, return electrode 112 is not directlyconnected to active electrodes 104. To complete a current path so thatactive electrodes 104 are electrically connected to return electrode112, electrically conductive fluid (e.g., isotonic saline) is caused toflow therebetween. In the representative embodiment, the electricallyconductive fluid is delivered through an external fluid tube 239 toopening 237, as described above. Alternatively, the fluid may bedelivered by a fluid delivery element (not shown) that is separate fromprobe 20. In some microendoscopic discectomy procedures, for example,the trocar cannula may be flooded with isotonic saline and the probe 20will be introduced into this flooded cavity. Electrically conductivefluid will be continually resupplied with a separate instrument tomaintain the conduction path between return electrode 112 and activeelectrodes 104.

[0146] In alternative embodiments, the fluid path may be formed in probe20 by, for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (not shown).This annular gap may be formed near the perimeter of the shaft 100 suchthat the electrically conductive fluid tends to flow radially inwardtowards the target site, or it may be formed towards the center of shaft100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 20 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in parentapplication U.S. Pat. No. 5,697,281, filed on Jun. 7, 1995 (AttorneyDocket 16238-0006000), the complete disclosure of which is incorporatedherein by reference.

[0147] Referring to FIG. 4, the electrically isolated active electrodes104 are spaced apart over tissue treatment surface 212 of electrodesupport member 102. The tissue treatment surface and individual activeelectrodes 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range ofabout 1 mm to 30 mm, usually about 2 mm to 20 mm. The individual activeelectrodes 104 preferably extend outward from tissue treatment surface212 by a distance of about 0.1 mm to 8 mm, usually about 0.2 mm to 4 mm.Applicant has found that this configuration increases the high electricfield intensities and associated current densities around activeelectrodes 104 to facilitate the ablation of tissue as described indetail above.

[0148] In the embodiment of FIGS. 2-5, the probe includes a single,larger opening 209 in the center of tissue treatment surface 212, and aplurality of active electrodes (e.g., about 3-15 electrodes) around theperimeter of surface 212 (see FIG. 3). Alternatively, the probe mayinclude a single, annular, or partially annular, active electrode at theperimeter of the tissue treatment surface. The central opening 209 iscoupled to a suction or aspiration lumen 213 (see FIG. 2) within shaft100 and a suction tube 211 (FIG. 2) for aspirating tissue, fluids and/orgases from the target site. In this embodiment, the electricallyconductive fluid generally flows from opening 237 of fluid tube 239radially inward past active electrodes 104 and then back through thecentral opening 209 of support member 102. Aspirating the electricallyconductive fluid during surgery allows the surgeon to see the targetsite, and it prevents the fluid from flowing into the patient's body,e.g., into the spine, the abdomen or the thoracic cavity. Thisaspiration should be controlled, however, so that the conductive fluidmaintains a conductive path between the active electrode(s) and thereturn electrode.

[0149] Of course, it will be recognized that the distal tip of probe mayhave a variety of different configurations. For example, the probe mayinclude a plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (this embodiment not shown in the drawings). Inthis embodiment, the active electrodes 104 extend from the center oftissue treatment surface 212 radially inward from openings 209. Theopenings are suitably coupled to fluid tube 233 for deliveringelectrically conductive fluid to the target site, and aspiration lumen213 for aspirating the fluid after it has completed the conductive pathbetween the return electrode 112 and the active electrodes 104.

[0150] In some embodiments, the probe 20 will also include one or moreaspiration electrode(s) coupled to the aspiration lumen for inhibitingclogging during aspiration of tissue fragments from the surgical site.As shown in FIG. 6, one or more of the active electrodes 104 maycomprise loop electrodes 140 that extend across distal opening 209 ofthe suction lumen within shaft 100. In the representative embodiment,two of the active electrodes 104 comprise loop electrodes 140 that crossover the distal opening 209. Of course, it will be recognized that avariety of different configurations are possible, such as a single loopelectrode, or multiple loop electrodes having different configurationsthan shown. In addition, the electrodes may have shapes other thanloops, such as the coiled configurations shown in FIGS. 6 and 7.Alternatively, the electrodes may be formed within suction lumenproximal to the distal opening 209, as shown in FIG. 8. The mainfunction of loop electrodes 140 is to ablate portions of tissue that aredrawn into the suction lumen to prevent clogging of the lumen.

[0151] Loop electrodes 140 are electrically isolated from the otheractive electrodes 104, which can be referred to hereinafter as theablation electrodes 104. Loop electrodes 140 may or may not beelectrically isolated from each other. Loop electrodes 140 will usuallyextend only about 0.05 mm to 4 mm, preferably about 0.1 mm to 1 mm fromthe tissue treatment surface of electrode support member 104.

[0152] Referring now to FIGS. 7 and 8, alternative embodiments foraspiration electrodes will now be described. As shown in FIG. 7, theaspiration electrodes may comprise a pair of coiled electrodes 150 thatextend across distal opening 209 of the suction lumen. The largersurface area of the coiled electrodes 150 usually increases theeffectiveness of the electrodes 150 on tissue fragments passing throughopening 209. In FIG. 8, the aspiration electrode comprises a singlecoiled electrode 154 passing across the distal opening 209 of suctionlumen. This single electrode 154 may be sufficient to inhibit cloggingof the suction lumen. Alternatively, the aspiration electrodes may bepositioned within the suction lumen proximal to the distal opening 209.Preferably, these electrodes are close to opening 209 so that tissuedoes not clog the opening 209 before it reaches electrode 154. In thisembodiment, a separate return electrode 156 may be provided within thesuction lumen to confine the electric currents therein.

[0153] Referring to FIG. 10, another embodiment of the present inventionincorporates an aspiration electrode 160 within the aspiration lumen 162of the probe. As shown, the electrode 160 is positioned just proximal ofdistal opening 209 so that the tissue fragments are ablated as theyenter lumen 162. In the representative embodiment, the aspirationelectrode 160 comprises a loop electrode that stretches across theaspiration lumen 162. However, it will be recognized that many otherconfigurations are possible.

[0154] In this embodiment, the return electrode 164 is located outsideof the probe as in the previously described embodiments. Alternatively,the return electrode(s) may be located within the aspiration lumen 162with the aspiration electrode 160. For example, the inner insulatingcoating 163 may be exposed at portions within the lumen 162 to provide aconductive path between this exposed portion of return electrode 164 andthe aspiration electrode 160. The latter embodiment has the advantage ofconfining the electric currents to within the aspiration lumen. Inaddition, in dry fields in which the conductive fluid is delivered tothe target site, it is usually easier to maintain a conductive fluidpath between the active and return electrodes in the latter embodimentbecause the conductive fluid is aspirated through the aspiration lumen162 along with the tissue fragments.

[0155] Referring to FIG. 9, another embodiment of the present inventionincorporates a wire mesh electrode 600 extending across the distalportion of aspiration lumen 162. As shown, mesh electrode 600 includes aplurality of openings 602 to allow fluids and tissue fragments to flowthrough into aspiration lumen 162. The size of the openings 602 willvary depending on a variety of factors. The mesh electrode may becoupled to the distal or proximal surfaces of ceramic support member102. Wire mesh electrode 600 comprises a conductive material, such asplatinum, titanium, tantalum, steel, stainless steel, tungsten, copper,gold or the like. In the representative embodiment, wire mesh electrode600 comprises a different material having a different electric potentialthan the active electrode(s) 104. Preferably, mesh electrode 600comprises steel and active electrode(s) 104 comprises tungsten.Applicant has found that a slight variance in the electrochemicalpotential of mesh electrode 600 and active electrode(s) 104 improves theperformance of the device. Of course, it will be recognized that themesh electrode may be electrically insulated from active electrode(s) asin previous embodiments

[0156] Referring now to FIGS. 11A-11C, an alternative embodimentincorporating a metal screen 610 is illustrated. As shown, metal screen610 has a plurality of peripheral openings 612 for receiving activeelectrodes 104, and a plurality of inner openings 614 for allowingaspiration of fluid and tissue through opening 609 of the aspirationlumen. As shown, screen 610 is press fitted over active electrodes 104and then adhered to shaft 100 of probe 20. Similar to the mesh electrodeembodiment, metal screen 610 may comprise a variety of conductivemetals, such as platinum, titanium, tantalum, steel, stainless steel,tungsten, copper, gold, or the like. In the representative embodiment,metal screen 610 is coupled directly to, or integral with, activeelectrode(s) 104. In this embodiment, the active electrode(s) 104 andthe metal screen 610 are electrically coupled to each other.

[0157] FIGS. 32A-B and 33A-C illustrate alternative embodiments of themesh and screen aspiration electrodes. As shown in FIGS. 32A and 32B,the probe may include a conductive cage electrode 620 that extends intothe aspiration lumen 162 (not shown) to increase the effect of theelectrode on aspirated tissue. FIGS. 33A-33C illustrate a dome-shapedscreen electrode 630 that includes one or more anchors 632 (four in therepresentative embodiment) for attaching the screen electrode 630 to aconductive spacer 634. Screen electrode 630 includes a plurality ofholes 631 for allowing fluid and tissue fragments to pass therethroughto aspiration lumen 162. Screen electrode 630 is sized to fit withinopening 609 of aspiration lumen 162 except for the anchors 632 whichinclude holes 633 for receiving active electrodes 104. Spacer 634includes peripheral holes 636 for receiving active electrodes 104 and acentral hole 638 aligned with suction lumen 162. Spacer 634 may furtherinclude insulated holes 640 for electrically isolating screen electrode630 from active electrodes 104. As shown in FIG. 33C, dome-shaped screenelectrode 630 preferably extends distally from the probe shaft 100 aboutthe same distance as the active electrodes 104. Applicant has found thatthis configuration enhances the ablation rate for tissue adjacent toactive electrodes 104, while still maintaining the ability to ablateaspirated tissue fragments passing through screen 630.

[0158]FIG. 5 illustrates the electrical connections 250 within handle204 for coupling active electrodes 104 and return electrode 112 to thepower supply 28. As shown, a plurality of wires 252 extend through shaft100 to couple electrodes 104 to a plurality of pins 254, which areplugged into a connector block 256 for coupling to a connecting cable 22(FIG. 1). Similarly, return electrode 112 is coupled to connector block256 via a wire 258 and a plug 260.

[0159] In some embodiments of the present invention, the probe 20further includes an identification element that is characteristic of theparticular electrode assembly so that the same power supply 28 can beused for different electrosurgical operations. In one embodiment, forexample, the probe 20 includes a voltage reduction element or a voltagereduction circuit for reducing the voltage applied between the activeelectrodes 104 and the return electrode 112. The voltage reductionelement serves to reduce the voltage applied by the power supply so thatthe voltage between the active electrodes and the return electrode islow enough to avoid excessive power dissipation into the electricallyconducting medium and/or ablation of the soft tissue at the target site.The voltage reduction element primarily allows the electrosurgical probe20 to be compatible with various generator or power supply models thatare adapted to apply higher voltages for ablation, moleculardissociation, or vaporization of tissue (e.g., generators supplied byArthroCare Corporation, Sunnyvale, Calif.). For contraction of tissue,for example, the voltage reduction element will serve to reduce avoltage of about 100 to 135 volts rms (which is a setting of 1 on theArthroCare Model 970 and 980 (i.e., 2000) Generators) to about 45 to 60volts rms, which is a suitable voltage for contraction of tissue withoutablation (e.g., without molecular dissociation) of the tissue.

[0160] Of course for some procedures in endoscopic spine surgery, theprobe will typically not require a voltage reduction element.Alternatively, the probe may include a voltage increasing element orcircuit, if desired.

[0161] In the representative embodiment, the voltage reduction elementcomprises a pair of capacitors forming a bridge divider (not shown)coupled to the power supply and coagulation electrode 380. Thecapacitors usually have a capacitance of about 200 pF to 500 pF (at 500volts) and preferably about 300 pF to 350 pF (at 500 volts). Of course,the capacitors may be located in other places within the system, such asin, or distributed along the length of, the cable, the generator, theconnector, etc. In addition, it will be recognized that other voltagereduction elements, such as diodes, transistors, inductors, resistors,capacitors or combinations thereof, may be used in conjunction with thepresent invention. For example, the probe 350 may include a codedresistor (not shown) that is constructed to lower the voltage appliedbetween the return and coagulation electrodes 360, 380, respectively. Inaddition, electrical circuits may be employed for this purpose.

[0162] Alternatively or additionally, the cable 22 that couples thepower supply 28 to probe 20/90 may be used as a voltage reductionelement. The cable has an inherent capacitance that can be used toreduce the power supply voltage if the cable is placed into theelectrical circuit between the power supply, the active electrodes andthe return electrode. In this embodiment, the cable 22 may be usedalone, or in combination with one of the voltage reduction elementsdiscussed above, e.g., a capacitor.

[0163] In some embodiments, probe 20/90 will further include a switch(not shown) or other input that allows the surgeon to couple anddecouple the identification element to the rest of the electronics inprobe 20/90. For example, if the surgeon would like to use the sameprobe for ablation of tissue and contraction of tissue in the sameprocedure, this can be accomplished by manipulating the switch. Thus,for ablation of tissue, the surgeon will decouple the voltage reductionelement from the electronics so that the full voltage applied by thepower source is applied to the electrodes on the probe. When the surgeondesires to reduce the voltage to a suitable level for contraction oftissue, he/she couples the voltage reduction element to the electronicsto reduce the voltage applied by the power supply to the activeelectrodes.

[0164] Further, it should be noted that the present invention can beused with a power supply that is adapted to apply a voltage within theselected range for treatment of tissue. In this embodiment, a voltagereduction element or circuitry may not be desired.

[0165] The present invention is particularly useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. As shown in FIGS. 12-15, a percutaneous penetration270 is made in the patients' back 272 so that the superior lamina 274can be accessed. Typically, a small needle (not shown) is used initiallyto localize the disc space level, and a guidewire (not shown) isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina 274. Sequential cannulated dilators 276 are inserted over theguide wire and each other to provide a hole from percutaneouspenetration 270 to the lamina 274. The first dilator may be used to“palpate” the lamina 274, assuring proper location of its tip betweenthe spinous process and facet complex just above the inferior edge ofthe lamina 274. As shown in FIG. 13, a tubular retractor 278 is thenpassed over the largest dilator down to the lamina 274. The dilators 276are removed, establishing an operating corridor within the. tubularretractor 278.

[0166] As shown in FIG. 13, an endoscope 280 is then inserted into thetubular retractor 278 and a ring clamp 282 is used to secure theendoscope 280. Typically, the formation of the operating corridor withinretractor 278 requires the removal of soft tissue, muscle or other typesof tissue that were forced into this corridor as the dilators 276 andretractor 278 were advanced down to the lamina 274. In procedures of theprior art, this tissue has usually been removed with mechanicalinstruments, such as pituitary rongeurs, curettes, graspers, cutters,drills, microdebriders and the like. Unfortunately, these mechanicalinstruments greatly lengthen and increase the complexity of theprocedure. In addition, these instruments sever blood vessels withinthis tissue, usually causing profuse bleeding that obstructs thesurgeon's view of the target site.

[0167] According to the present invention, an electrosurgical probe orcatheter 284 as described above is introduced into the operatingcorridor within the retractor 278 to remove the soft tissue, muscle andother obstructions from this corridor so that the surgeon can easilyaccess and visualize the lamina 274. Once the surgeon has introduced theprobe 284, electrically conductive fluid 285 is delivered through tube233 and opening 237 to the tissue (see FIG. 2). The fluid flows past thereturn electrode 112 to the active electrodes 104 at the distal end ofthe shaft. The rate of fluid flow is controlled with valve 17 (FIG. 1)such that the zone between the tissue and electrode support 102 isconstantly immersed in the fluid. The power supply 28 is then turned onand adjusted such that a high frequency voltage difference is appliedbetween active electrodes 104 and return electrode 112. The electricallyconductive fluid provides the conduction path (see current flux lines)between active electrodes 104 and the return electrode 112.

[0168] The high frequency voltage is sufficient to convert theelectrically conductive fluid (not shown) between the target tissue andactive electrode(s) 104 into an ionized vapor layer or plasma (notshown). As a result of the applied voltage difference between activeelectrode(s) 104 and the target tissue (i.e., the voltage gradientacross the plasma layer), charged particles in the plasma (e.g.,electrons) cause dissociation of the molecular bonds within tissuestructures. This molecular dissociation is accompanied by the volumetricremoval (i.e., ablative sublimation) of tissue and the production of lowmolecular weight gases, such as oxygen, nitrogen, carbon dioxide,hydrogen and methane. This process can be precisely controlled to effectthe volumetric removal of tissue as thin as 10 microns to 150 micronswith minimal heating of, or damage to, underlying tissue structures. Amore detailed description of this phenomenon is presented in commonlyassigned U.S. Pat. No. 5,697,882, the complete disclosure of which isincorporated herein by reference.

[0169] During the process, the gases will be aspirated through opening209 and suction tube 211 to a vacuum source. In addition, excesselectrically conductive fluid, and other fluids (e.g., blood) will beaspirated from the operating corridor to facilitate the surgeon's view.During ablation of the tissue, the residual heat generated by thecurrent flux lines (typically less than 150° C.), will usually besufficient to coagulate any severed blood vessels at the site. If not,the surgeon may switch the power supply 28 into the coagulation mode bylowering the voltage to a level below the threshold for fluidvaporization, as discussed above. This simultaneous hemostasis resultsin less bleeding and facilitates the surgeon's ability to perform theprocedure.

[0170] Another advantage of the present invention is the ability toprecisely ablate soft tissue without causing necrosis or thermal damageto the underlying and surrounding tissues, nerves or bone. In addition,the voltage can be controlled so that the energy directed to the targetsite is insufficient to ablate the lamina 274 so that the surgeon canliterally clean the tissue off the lamina 274, without ablating orotherwise effecting significant damage to the lamina.

[0171] Referring now to FIGS. 14 and 15, once the operating corridor issufficiently cleared, a laminotomy and medial facetectomy isaccomplished either with conventional techniques (e.g., a Kerrison punchor a high speed drill) or with the electrosurgical probe 284 asdiscussed above. After the nerve root is identified, medical retractioncan be achieved with a retractor 288, or the present invention can beused to ablate with precision the disc. If necessary, epidural veins arecauterized either automatically or with the coagulation mode of thepresent invention. If an annulotomy is necessary, it can be accomplishedwith a microknife or the ablation mechanism of the present inventionwhile protecting the nerve root with the retractor 288. The herniateddisc 290 is then removed with a pituitary rongeur in a standard fashion,or once again through ablation as described above.

[0172] In another embodiment, the electrosurgical probe of the presentinvention can be used to ablate and/or contract soft tissue within thedisc 290 to allow the annulus 292 to repair itself to preventreoccurrence of this procedure. For tissue contraction, a sufficientvoltage difference is applied between the active electrodes 104 and thereturn electrode 112 to elevate the tissue temperature from normal bodytemperatures (e.g., 37° C.) to temperatures in the range of 45° C. to90° C., preferably in the range from 60° C. to 70° C. This temperatureelevation causes contraction of the collagen connective fibers withinthe disc tissue so that the nucleus pulposus 291 withdraws into theannulus fibrosus 292.

[0173] In one method of tissue contraction according to the presentinvention, an electrically conductive fluid is delivered to the targetsite as described above, and heated to a sufficient temperature toinduce contraction or shrinkage of the collagen fibers in the targettissue. The electrically conductive fluid is heated to a temperaturesufficient to substantially irreversibly contract the collagen fibers,which generally requires a tissue temperature in the range of about 45°C. to 90° C., usually about 60° C. to 70° C. The fluid is heated byapplying high frequency electrical energy to the active electrode(s) incontact with the electrically conducting fluid. The current emanatingfrom the active electrode(s) 104 heats the fluid and generates a jet orplume of heated fluid, which is directed towards the target tissue. Theheated fluid elevates the temperature of the collagen sufficiently tocause hydrothermal shrinkage of the collagen fibers. The returnelectrode 112 draws the electric current away from the tissue site tolimit the depth of penetration of the current into the tissue, therebyinhibiting molecular dissociation and breakdown of the collagen tissueand minimizing or completely avoiding damage to surrounding andunderlying tissue structures beyond the target tissue site. In anexemplary embodiment, the active electrode(s) 104 are held away from thetissue a sufficient distance such that the RF current does not pass intothe tissue at all, but rather passes through the electrically conductivefluid back to the return electrode. In this embodiment, the primarymechanism for imparting energy to the tissue is the heated fluid, ratherthan the electric current.

[0174] In an alternative embodiment, the active electrode(s) 104 arebrought into contact with, or close proximity to, the target tissue sothat the electric current passes directly into the tissue to a selecteddepth. In this embodiment, the return electrode draws the electriccurrent away from the tissue site to limit its depth of penetration intothe tissue. Applicant has discovered that the depth of currentpenetration can also be varied with the electrosurgical system of thepresent invention by changing the frequency of the voltage applied tothe active electrode and the return electrode. This is because theelectrical impedance of tissue is known to decrease with increasingfrequency due to the electrical properties of cell membranes whichsurround electrically conductive cellular fluid. At lower frequencies(e.g., less than 350 kHz), the higher tissue impedance, the presence ofthe return electrode and the active electrode configuration of thepresent invention (discussed in detail below) cause the current fluxlines to penetrate less deeply resulting in a smaller depth of tissueheating. In an exemplary embodiment, an operating frequency of about 100to 200 kHz is applied to the active electrode(s) to obtain shallowdepths of collagen shrinkage (e.g., usually less than 1.5 mm andpreferably less than 0.5 mm).

[0175] In another aspect of the invention, the size (e.g., diameter orprincipal dimension) of the active electrodes employed for treating thetissue are selected according to the intended depth of tissue treatment.As described previously in copending patent application PCTInternational Application, U.S. National Phase Serial No.PCT/US94/05168, the depth of current penetration into tissue increaseswith increasing dimensions of an individual active electrode (assumingother factors remain constant, such as the frequency of the electriccurrent, the return electrode configuration, etc.). The depth of currentpenetration (which refers to the depth at which the current density issufficient to effect a change in the tissue, such as collagen shrinkage,irreversible necrosis, etc.) is on the order of the active electrodediameter for the bipolar configuration of the present invention andoperating at a frequency of about 100 kHz to about 200 kHz. Accordingly,for applications requiring a smaller depth of current penetration, oneor more active electrodes of smaller dimensions would be selected.Conversely, for applications requiring a greater depth of currentpenetration, one or more active electrodes of larger dimensions would beselected.

[0176] FIGS. 16-18 illustrate an alternative electrosurgical system 300specifically configured for endoscopic discectomy procedures, e.g., fortreating extruded or non-extruded herniated discs. As shown in FIG. 16system 300 includes a trocar cannula 302 for introducing a catheterassembly 304 through a percutaneous penetration in the patient to atarget disc in the patient's spine. As discussed above, the catheterassembly 304 may be introduced through the thorax in a thoracoscopicprocedure, through the abdomen in a laparascopic procedure, or directlythrough the patient's back. Catheter assembly 304 includes a catheterbody 306 with a plurality of inner lumens (not shown) and a proximal hub308 for receiving the various instruments that will pass throughcatheter body 306 to the target site. In this embodiment, assembly 304includes an electrosurgical instrument 310 with a flexible shaft 312, anaspiration catheter 314, an endoscope 316 and an illumination fibershaft 318 for viewing the target site. As shown in FIGS. 16 and 17,aspiration catheter 314 includes a distal port 320 and a proximalfitment 322 for attaching catheter 314 to a source of vacuum (notshown). Endoscope 316 will usually comprise a thin metal tube 317 with alens 324 at the distal end, and an eyepiece (not shown) at the proximalend.

[0177] In the exemplary embodiment, electrosurgical instrument 310includes a twist locking stop 330 at a proximal end of the shaft 312 forcontrolling the axial travel distance T_(D) of the probe. As discussedin detail below, this configuration allows the surgeon to “set” thedistance of ablation within the disc. In addition, instrument 310includes a rotational indicator 334 for displaying the rotationalposition of the distal portion of instrument 310 to the surgeon. Thisrotational indicator 334 allows the surgeon to view this rotationalposition without relying on the endoscope 316 if visualization isdifficult, or if an endoscope is not being used in the procedure.

[0178] Referring now to FIGS. 17 and 18, a distal portion 340 ofelectrosurgical instrument 310 and catheter body 306 will now bedescribed. As shown, instrument 310 comprises a relatively stiff, butdeflectable electrically insulating support cannula 312 and a workingend portion 348 movably coupled to cannula 312 for rotational andtranslational movement of working end 348. Working end 348 ofelectrosurgical instrument 310 can be rotated and translated to ablateand remove a volume of nucleus pulposus within a disc. Support cannula312 extends through an internal lumen 344 and beyond the distal end 346of catheter body 306. Alternatively, support cannula 312 may be separatefrom instrument 310, or even an integral part of catheter body 306. Thedistal portion of working end 348 includes an exposed return electrode350 separated from an active electrode array 352 by an insulatingsupport member 354, such as ceramic. In the representative embodiment,electrode array 352 is disposed on only one side of ceramic supportmember 354 so that its other side is insulating and thus atraumatic totissue. Instrument 310 will also include a fluid lumen (not shown)having a distal port 360 in working end 348 for delivering electricallyconductive fluid to the target site.

[0179] In use, trocar cannula 302 is introduced into a percutaneouspenetration suitable for endoscopic delivery to the target disc in thespine. A trephine (not shown) or other conventional instrument may beused to form a channel from the trocar cannula 302 through the annulusfibrosus 292 and into the nucleus pulposus. Alternatively, the probe 310may be used for this purpose, as discussed above. The working end 348 ofinstrument 310 is then advanced through cannula 302 a short distance(e.g., about 7 to 10 mm) into the nucleus pulposus 291, as shown in FIG.18. Once the electrode array 352 is in position, electrically conductivefluid is delivered through distal port 360 to immerse the activeelectrode array 352 in the fluid. The vacuum source may also beactivated to ensure a flow of conductive fluid between electrode array352 past return electrode 350 to suction port 320, if necessary. In someembodiments, the mechanical stop 330 may then be set at the proximal endof the instrument 310 to limit the axial travel distance of working end348. Preferably, this distance will be set to minimize (or completelyeliminate) ablation of the surrounding annulus.

[0180] The probe is then energized by applying high frequency voltagedifference between the electrode array 352 and return electrode 350 sothat electric current flows through the conductive fluid from the array352 to the return electrode 350. The electric current causesvaporization of the fluid and ensuing molecular dissociation of thenucleus pulposus tissue as described in detail above. The instrument 310may then be translated in an axial direction forwards and backwards tothe preset limits. While still energized and translating, the workingend 348 may also be rotated to ablate tissue surrounding the electrodearray 352. In the representative embodiment, working end 348 will alsoinclude an inflatable gland 380 opposite electrode array 352 to allowdeflection of working end 348 relative to support cannula 312. As shownin FIG. 18, working end 348 may be deflected to produce a large diameterbore within the nucleus pulposus, which assures close contact withtissue surfaces to be ablated. Alternatively, the entire catheter body306, or the distal end of catheter body 306 may be deflected to increasethe volume of nucleus pulposus removed.

[0181] After the desired volume of nucleus pulposus is removed (based ondirect observation through port 324, or by kinesthetic feedback frommovement of working end 348 of instrument 310), instrument 310 iswithdrawn into catheter body 306 and the catheter body is removed fromthe patient. Typically, the preferred volume of removed tissue is about0.2 cm³ to 5.0 cm³.

[0182] Referring now to FIGS. 19-28, alternative systems and methods forablating tissue in confined (e.g., narrow) body spaces will now bedescribed. FIG. 19 illustrates an exemplary planar ablation probe 400according to the present invention. Similar to the instruments describedabove, probe 400 can be incorporated into electrosurgical system 11 (orother suitable systems) for operation in either the bipolar or monopolarmodalities.

[0183] Probe 400 generally includes a support member 402, a distalworking end 404 attached to the distal end of support member 402 and aproximal handle 406 attached to the proximal end of support member 402.As shown in FIG. 19, handle 406 includes a handpiece 408 and a powersource connector 410 removably coupled to handpiece 408 for electricallyconnecting working end 404 with power supply 28 through cable 34 (seeFIG. 1).

[0184] In the embodiment shown in FIG. 19, planar ablation probe 400 isconfigured to operate in the bipolar modality. Accordingly, supportmember 402 or a portion thereof functions as the return electrode andcomprises an electrically conducting material, such as titanium, oralloys containing one or more of nickel, chromium, iron, cobalt, copper,aluminum, platinum, molybdenum, tungsten, tantalum or carbon. In thepreferred embodiment, support member 402 is an austenitic stainlesssteel alloy, such as stainless steel Type 304 from MicroGroup, Inc.,Medway, Mass. As shown in FIG. 19, support member 402 is substantiallycovered by an insulating layer 412 to prevent electric current fromdamaging surrounding tissue. An exposed portion 414 of support member402 functions as the return electrode for probe 400. Exposed portion 414is preferably spaced proximally from active electrodes 416 by a distanceof about 1 mm to 20 mm.

[0185] Referring to FIGS. 20 and 21, planar ablation probe 400 furthercomprises a plurality of active electrodes 416 extending from anelectrically insulating spacer 418 at the distal end of support member402. Of course, it will be recognized that probe 400 may include asingle electrode depending on the size of the target tissue to betreated and the accessibility of the treatment site (see FIG. 26, forexample). Insulating spacer 418 is preferably bonded to support member402 with a suitable epoxy adhesive 419 to form a mechanical bond and afluid-tight seal. Electrodes 416 usually extend about 2.0 mm to 20 mmfrom spacer 418, and preferably less than 10 mm. A support tongue 420extends from the distal end of support member 402 to support activeelectrodes 416. Support tongue 420 and active electrodes 416 have asubstantially low profile to facilitate accessing narrow spaces withinthe patient's body, such as the spaces between adjacent vertebrae andbetween articular cartilage and the meniscus in the patient's knee.Accordingly, tongue 420 and electrodes 416 have a substantially planarprofile, usually having a combined height He of less than 4.0 mm,preferably less than 2.0 mm and more preferably less than 1.0 mm (seeFIG. 25). In the case of ablation of meniscus near articular cartilage,the height He of both the tongue 420 and electrodes 416 is preferablybetween about 0.5 mm to 1.5 mm. The width of electrodes 416 and supporttongue 420 will usually be less than 10.0 mm and preferably betweenabout 2.0 mm to 4.0 mm.

[0186] Support tongue 420 includes a “non-active” surface 422 opposingactive electrodes 416 covered with an electrically insulating layer (notshown) to minimize undesirable current flow into adjacent tissue orfluids. Non-active surface 422 is preferably atraumatic, i.e., having asmooth planar surface with rounded corners, to minimize unwanted injuryto tissue or nerves in contact therewith, such as disc tissue or thenearby spinal nerves, as the working end of probe 400 is introduced intoa narrow, confined body space. Non-active surface 422 of tongue 420 helpto minimize iatrogenic injuries to tissue and nerves so that working end404 of probe 400 can safely access confined spaces within the patient'sbody.

[0187] Referring to FIGS. 21A-B and 22, an electrically insulatingsupport member 430 is disposed between support tongue 420 and activeelectrodes 416 to inhibit or prevent electric current from flowing intotongue 420. Insulating member 430 and insulating layer 412 preferablycomprise a ceramic, glass or glass ceramic material, such as alumina.Insulating member 430 is mechanically bonded to support tongue 420 witha suitable epoxy adhesive to electrically insulate active electrodes 416from tongue 420. As shown in FIG. 26, insulating member 430 may overhangsupport tongue 420 to increase the electrical path length between theactive electrodes 416 and the insulation covered support tongue 420.

[0188] As shown in FIGS. 21A-23, active electrodes 416 are preferablyconstructed from a hollow, round tube, with at least the distal portion432 of electrodes 416 being filed off to form a semi-cylindrical tubewith first and second ends 440, 442 facing away from support tongue 420.Preferably, the proximal portion 434 of electrodes 416 will remaincylindrical to facilitate the formation of a crimp-type electricalconnection between active electrodes 416 and lead wires 450 (see FIG.23). As shown in FIG. 26, cylindrical proximal portions 434 ofelectrodes 416 extend beyond spacer 418 by a slight distance of 0.1 mmto 0.4 mm. The semi-cylindrical configuration of distal electrodeportion 432 increases the electric field intensity and associatedcurrent density around the edges of ends 440, 442, as discussed above.Alternatively, active electrodes 416 may have any of the shapes andconfigurations described above or other configurations, such as squarewires, triangular shaped wires, U-shaped or channel shaped wires and thelike. In addition, the surface of active electrodes 416 may beroughened, e.g., by grit blasting, chemical or electrochemical etching,to further increase the electric field intensity and associated currentdensity around distal portions 432 of electrodes 416.

[0189] As shown in FIG. 24, each lead wire 450 terminates at a connectorpin 452 contained in a pin insulator block 454 within handpiece 408.Lead wires 450 are covered with an insulation layer (not shown), e.g.,Tefzel™, and sealed from the inner portion of support member 402 with anadhesive seal 457 (FIG. 22). In the preferred embodiment, each electrode416 is coupled to a separate source of voltage within power supply 28.To that end, connector pins 452 are removably coupled to matingreceptacles 456 within connector 410 to provide electrical communicationwith active electrodes 416 and power supply 28 (FIG. 1). Electricallyinsulated lead wires 458 connect receptacles 456 to the correspondingsources of voltage within power supply 28. The electrically conductivewall 414 of support member 402 serves as the return electrode, and issuitably coupled to one of the lead wires 450.

[0190] In an alternative embodiment, adjacent electrodes 416 may beconnected to the opposite polarity of source 28 so that current flowsbetween adjacent active electrodes 416 rather than between activeelectrodes 416 and return electrode 414. By way of example, FIG. 21Billustrates a distal portion of a planar ablation probe 400′ in whichelectrodes 416 a and 416 c are at one voltage polarity (i.e., positive)and electrodes 416 b and 416 d are at the opposite voltage polarity(negative). When a high frequency voltage is applied between electrodes416 a, 416 c and electrodes 416 b, 416 d in the presence of electricallyconductive liquid, current flows between electrodes 416 a, 416 c and 416b, 416 d as illustrated by current flux lines 522′. Similar to the aboveembodiments, the opposite surface 420 of working end 404′ of probe 400′is generally atraumatic and electrically insulated from activeelectrodes 416 a, 416 b, 416 c and 416 d to minimize unwanted injury totissue in contact therewith.

[0191] In an exemplary configuration, each source of voltage includes acurrent limiting element or circuitry (not shown) to provide independentcurrent limiting based on the impedance between each individualelectrode 416 and return electrode 414. The current limiting elementsmay be contained within the power supply 28, the lead wires 450, cable34, handle 406, or within portions of the support member 402 distal tohandle 406. By way of example, the current limiting elements may includeresistors, capacitors, inductors, or a combination thereof.Alternatively, the current limiting function may be performed by (1) acurrent sensing circuit which causes the interruption of current flow ifthe current flow to the electrode exceeds a predetermined value and/or(2) an impedance sensing circuit which causes the interruption ofcurrent flow (or reduces the applied voltage to zero) if the measuredimpedance is below a predetermined value. In another embodiment, two ormore of the electrodes 416 may be connected to a single lead wire 450such that all of the electrodes 416 are always at the same appliedvoltage relative to return electrode 414. Accordingly, any currentlimiting elements or circuits will modulate the current supplied or thevoltage applied to the array of electrodes 416, rather than limitingtheir current individually, as discussed in the previous embodiment.

[0192] Referring to FIGS. 25-28, methods for ablating tissue structureswith planar ablation probe 400 according to the present invention willnow be described. In particular, exemplary methods for treating adiseased meniscus within the knee (FIGS. 29-31) and for removing softtissue between adjacent vertebrae in the spine (FIG. 32) will bedescribed. In both procedures, at least the working end 404 of planarablation probe 400 is introduced to a treatment site either by minimallyinvasive techniques or open surgery. Electrically conductive liquid isdelivered to the treatment site, and voltage is applied from powersupply 28 between active electrodes 416 and return electrode 414. Thevoltage is preferably sufficient to generate electric field intensitiesnear active electrodes that form a vapor layer in the electricallyconductive liquid, and induce the discharge of energy from the vaporlayer to ablate tissue at the treatment site, as described in detailabove.

[0193] Referring to FIG. 25, working end 404 and at least the distalportion of support member 402 are introduced through a percutaneouspenetration 500, such as a cannula, into the arthroscopic cavity 502.The insertion of probe 400 is usually guided by an arthroscope (notshown) which includes a light source and a video camera to allow thesurgeon to selectively visualize a zone within the knee joint. Tomaintain a clear field of view and to facilitate the generation of avapor layer, a transparent, electrically conductive irrigant 503, suchas isotonic saline, is injected into the treatment site either through aliquid passage in support member 402 of probe 400, or through anotherinstrument. Suitable methods for delivering irrigant to a treatment siteare described in commonly assigned U.S. Pat. No. 5,697,281 filed on Jun.7, 1995 (Attorney Docket 16238-000600), the contents of which areincorporated herein by reference.

[0194] In the example shown in FIG. 25, the target tissue is a portionof the meniscus 506 adjacent to and in close proximity with thearticular cartilage 510, 508 which normally covers the end surfaces ofthe tibia 512 and the femur 514, respectively. The articular cartilage508, 510 is important to the normal functioning of joints, and oncedamaged, the body is generally not capable of regenerating this criticallining of the joints. Consequently, it is desirable that the surgeonexercise extreme care when treating the nearby meniscus 506 to avoidunwanted damage to the articular cartilage 508, 510. The confined spaces513 between articular cartilage 508, 510 and meniscus 506 within theknee joint are relatively narrow, typically on the order of about 1.0 mmto 5.0 mm. Accordingly, the narrow, low profile working end 404 ofablation probe 400 is ideally suited for introduction into theseconfined spaces 513 to the treatment site. As mentioned previously, thesubstantially planar arrangement of electrodes 416 and support tongue420 (typically having a combined height of about 0.5 to 1.5 mm) allowsthe surgeon to deliver working end 404 of probe 400 into the confinedspaces 513, while minimizing contact with the articular cartilage 508,510 (see FIG. 26).

[0195] As shown in FIG. 26, active electrodes 416 are disposed on oneface of working end 404 of probe 400. Accordingly, a zone 520 of highelectric field intensity is generated on each electrode 416 on one faceof working end 404 while the opposite side 521 of working end 404 isatraumatic with respect to tissue. In addition, the opposite side 521 isinsulated from electrodes 416 to minimize electric current from passingthrough this side 521 to the tissue (i.e., adjacent articular cartilage508). As shown in FIGS. 26, the bipolar arrangement of active electrodes416 and return electrode 414 causes electric current to flow along fluxlines 522 predominantly through the electrically conducting irrigant503, which envelops the tissue and working end 404 of ablation probe 400and provides an electrically conducting path between electrodes 416 andreturn electrode 414. As electrodes 416 are engaged with, or positionedin close proximity to, the target meniscus 506, the high electric fieldpresent at the electrode edges cause controlled ablation of the tissueby forming a vapor layer and inducing the discharge of energy therefrom.In addition, the motion of electrodes 416 relative to the meniscus 506(as shown by vector 523) causes tissue to be removed in a controlledmanner. The presence of the irrigant also serves to minimize theincrease in the temperature of the meniscus during the ablation processbecause the irrigant generally comes in contact with the treated tissueshortly after one of the electrodes 416 has been translated across thesurface of the tissue.

[0196] Referring now to FIG. 28, an exemplary method for removing softtissue 540 from the surfaces of adjacent vertebrae 542, 544 in the spinewill now be described. Removal of this soft tissue 540 is oftennecessary, for example, in surgical procedures for fusing or joiningadjacent vertebrae together. Following the removal of tissue 540, theadjacent vertebrae 542, 544 are stabilized to allow for subsequentfusion together to form a single monolithic vertebra. As shown, thelow-profile of working end 404 of probe 400 (i.e., thickness values aslow as 0.2 mm) allows access to and surface preparation of closelyspaced vertebrae. In addition, the shaped electrodes 416 promotesubstantially high electric field intensities and associated currentdensities between active electrodes 416 and return electrode 414 toallow for the efficient removal of tissue attached to the surface ofbone without significantly damaging the underlying bone. The“non-active” insulating side 521 of working end 404 also minimizes thegeneration of electric fields on this side 521 to reduce ablation of theadjacent vertebra 542.

[0197] The target tissue is generally not completely immersed inelectrically conductive liquid during surgical procedures within thespine, such as the removal of soft tissue described above. Accordingly,electrically conductive liquid will preferably be delivered into theconfined spaces 513 between adjacent vertebrae 542, 544 during thisprocedure. The fluid may be delivered through a liquid passage (notshown) within support member 402 of probe 400, or through anothersuitable liquid supply instrument.

[0198] Other modifications and variations can be made to discloseembodiments without departing from the subject invention as defined inthe following claims. For example, it should be clearly understood thatthe planar ablation probe 400 described above may incorporate a singleactive electrode, rather than a plurality of such active electrodes asdescribed above in the exemplary embodiment. FIG. 27 illustrates aportion of a planar ablation probe according to the present inventionthat incorporates a single active electrode 416′ for generating highelectric field densities 550 to ablate a target tissue 552. Electrode416′ may extend directly from a proximal support member, as depicted inFIG. 31, or it may be supported on an underlying support tongue (notshown) as described in the previous embodiment. As shown, therepresentative single active electrode 416′ has a semi-cylindricalcross-section, similar to the electrodes 416 described above. However,the single electrode 416′ may also incorporate any of the abovedescribed configurations (e.g., square or star shaped solid wire) orother specialized configurations depending on the function of thedevice.

[0199] Referring now to FIGS. 29-31 an alternative electrode supportmember 500 for a planar ablation probe 404 will be described in detail.As shown, electrode support member 500 preferably comprises a multilayeror single layer substrate 502 comprising a suitable high temperature,electrically insulating material, such as ceramic. The substrate 502 isa thin or thick film hybrid having conductive strips that are adheredto, e.g., plated onto, the ceramic wafer. The conductive stripstypically comprise tungsten, gold, nickel or equivalent materials. Inthe exemplary embodiment, the conductive strips comprise tungsten, andthey are co-fired together with the wafer layers to form an integralpackage. The conductive strips are coupled to external wire connectorsby holes or vias that are drilled through the ceramic layers, and platedor otherwise covered with conductive material.

[0200] In the representative embodiment, support member 500 comprises asingle ceramic wafer having a plurality of longitudinal ridges 504formed on one side of the wafer 502. Typically, the wafer 502 is greenpressed and fired to form the required topography (e.g., ridges 504). Aconductive material is then adhered to the ridges 504 to form conductivestrips 506 extending axially over wafer 502 and spaced from each other.As shown in FIG. 30, the conductive strips 506 are attached to leadwires 508 within shaft 412 of the probe 404 to electrically coupleconductive strips 506 with the power supply 28 (FIG. 1). This embodimentprovides a relatively low profile working end of probe 404 that hassufficient mechanical structure to withstand bending forces during asurgical procedure.

[0201] FIGS. 34-36 illustrate another system and method for treatingswollen or herniated intervertebral discs according to the presentinvention. In this procedure, an electrosurgical probe 700 comprises along, thin shaft 702 (e.g., on the order of about 1 mm or less indiameter) that can be percutaneously introduced posteriorly through thepatient's back directly into the spine. The probe shaft 702 will includeone or more active electrode(s) 704 for applying electrical energy totissues within the spine. The probe 700 may include one or more returnelectrodes 706, or the return electrode may be positioned on thepatient's back as a dispersive pad (not shown).

[0202] As shown in FIG. 34, the distal portion of shaft 702 isintroduced posteriorly through a small percutaneous penetration into theannulus 292 of the target intervertebral disc 290. To facilitate thisprocess, the distal end of shaft 702 may taper down to a sharper point(e.g., a needle), which can then be retracted to expose activeelectrode(s) 704. Alternatively, the active electrode(s) may be formedaround the surface of the tapered distal portion of shaft 702 (notshown). In either embodiment, the distal end of shaft 702 is deliveredthrough the annulus 292 to the target nucleus pulposus 291, which may beherniated, extruded, non-extruded, or simply swollen. As shown in FIG.35, high frequency voltage is applied between active electrode(s) 704and return electrode(s) 706 to heat the surrounding collagen to suitabletemperatures for contraction (i.e., typically about 55° C. to about 70°C.). As discussed above, this procedure may be accomplished with amonopolar configuration, as well. However, applicant has found that thebipolar configuration shown in FIGS. 34-36 provides enhanced control ofthe high frequency current, which reduces the risk of spinal nervedamage.

[0203] As shown in FIGS. 35 and 36, once the nucleus pulposus 291 hasbeen sufficiently contracted to retract from impingement on a nerve ornerve root, probe 700 is removed from the target site. In therepresentative embodiment, the high frequency voltage is applied betweenactive and return electrode(s) 704, 706 as the probe is withdrawnthrough the annulus 292. This voltage is sufficient to cause contractionof the collagen fibers within the annulus 292, which allows the annulus292 to contract around the hole formed by probe 700, thereby improvingthe healing of this hole. Thus, the probe 700 seals its own passage asit is withdrawn from the disc.

[0204]FIGS. 37A to 39 illustrate systems and methods for treating andablating intervertebral discs according to the present invention.Electrosurgical probe 800 generally comprises a shaft 802 that can bepercutaneously introduced posteriorly (through the patient's back) intothe spine. The shaft 802 will include one or more active electrode(s)804 for applying electrical energy to the intervertebral disc. Thesystem may include one or more return electrodes 806. The returnelectrode(s) 806 can be positioned proximal of the active electrode(s)804 on the electrosurgical probe or on a separate instrument (notshown). The ablation probe 800 shown in FIG. 37A is configured tooperate in the bipolar modality. In alternative embodiments, however,the return electrode 806 may be positioned on the patient's back as adispersive pad (not shown) so as to operate in a monopolar modality.

[0205] In the exemplary embodiment shown in FIGS. 37A and 37B, thedistal end of the shaft 802 is curved or bent to improve access to thedisk being treated. The treatment surface 808 of the electrosurgicalprobe is usually curved or bent to an angle of about 10 degrees to 90degrees relative to the longitudinal axis of shaft 802, preferably about15 degrees to 60 degrees and more preferably about 15 degrees. Inalternative embodiments, the distal portion of shaft 802 comprises aflexible material which can be deflected relative to the longitudinalaxis of the shaft. Such deflection may be selectively induced bymechanical tension of a pull wire, for example, or by a shape memorywire that expands or contracts by externally applied temperaturechanges. A more complete description of this embodiment can be found inU.S. Pat. No. 5,697,909, the complete disclosure of which isincorporated herein by reference. Alternatively, the shaft 802 of thepresent invention may be bent by the physician to the appropriate angleusing a conventional bending tool or the like.

[0206] The active electrode(s) 804 typically extend from an activetissue treatment surface of an electrode support member 810 of the probeshaft 802. Opposite of the active electrodes 802 is a non-activeinsulating side 812, which has an insulator 814 that is configured toprotect the dura mater 816 and other non-target tissue, e.g., spinalcord 818. The insulator 814 minimizes the generation of electric fieldson the non-active side and reduces the electrical damage to the duramater 816 and spinal cord 818 during disc ablation. While the insulator814 is shown opposite the active electrode array 804, it will beappreciated that the insulator 814 can be positioned completely aroundthe probe, be positioned around only portions of the probe, be along thesides of the active electrode array, and the like.

[0207] The tissue treatment surface 808 and individual active electrodes804 will usually have dimensions within the ranges set forth above. Insome embodiments, the active electrodes 804 can be disposed within or onan insulating support member 810, as described above. In therepresentative embodiment, the surface of the active electrodes 804 hasa circular cross-sectional shape with a diameter in the range of about 1mm to 30 mm, usually about 2 mm to 20 mm. The individual activeelectrodes 802 preferably extend outward from tissue treatment surface808 by a distance of about 0.1 mm to 8 mm, usually about 0.2 mm to 4 mm.Applicant has found that this configuration increases the electric fieldintensities and associated current densities around active electrodes804 to facilitate the ablation of tissue as described in detail above.Of course, it will be recognized that the active electrodes may have avariety of different configurations. For example, instead of an array ofactive electrodes, a single active electrode may be used.

[0208] An exemplary method for ablating and removing at least a portionof the target intervertebral disc 290 will now be described. Removal ofa degenerative or damaged disc is necessary, for example, in surgicalprocedures during placement of a cage, or the fusing or joining ofadjacent vertebrae together. Following the removal of the disc 290, theadjacent vertebrae 824 are stabilized to allow for subsequent fusiontogether to form a single monolithic vertebra. During such procedures itwould be preferable to protect the dura mater 816 and spinal cord 818from damage from the electrosurgical probe 800.

[0209] In use, the distal end of probe 800 is introduced into atreatment site either by minimally invasive techniques or open surgery.The distal portion of electrosurgical probe 800 can be introducedthrough a percutaneous penetration 826 e.g., via a camiula, into thebody cavity 828. The insertion of probe 800 is usually guided by anendoscope (not shown) which can include a light source and a videocamera to allow the surgeon to selectively visualize a zone within thevertebral column. The distal portion of shaft 802 can be introducedposteriorly through a small percutaneous penetration into the annulusfibrosus 292 of the target intervertebral disc 290 (FIGS. 38 and 39).

[0210] To maintain a clear field of view and to facilitate thegeneration of a vapor layer, a transparent, electrically conductiveirrigant (not shown), such as isotonic saline, can be injected into thetreatment site either through a liquid passage in probe 800, or throughanother instrument. Suitable methods for delivering irrigant to atreatment site are described in commonly assigned, U.S. Pat. No.5,697,281 filed on Jun. 7, 1995 (Attorney Docket 16238-000600), thecontents of which are incorporated herein by reference.

[0211] After (or during) introduction of the electrosurgical probe 800into the intervertebral disc 290, an electrically conductive liquid 830can be delivered to the treatment site, and voltage can be applied frompower supply 28 between active electrodes 804 and return electrode 806through the conductive fluid. The voltage is preferably sufficient togenerate electric field intensities near active electrodes 804 that forma vapor layer in the electrically conductive liquid so as to induce adischarge of energy from the vapor layer to ablate tissue at thetreatment site, as described in detail above. As shaft 802 is movedthrough the spinal disc 290, the insulator 814 can be positioned toengage the dura mater 816 and protect the dura mater 816 (and spinalcord 818) from damaging electrical current flow.

[0212] FIGS. 40 to 41 show yet another embodiment of the presentinvention. The electrosurgical probe 800 includes an aspiration lumen832 for aspirating the target area and a fluid delivery lumen 834 fordirecting an electrically conductive fluid 830 to the target area. Insome implementations, the aspiration lumen 832 and the fluid deliverylumen 834 are coupled together in an annular pattern along the exteriorof the electrosurgical probe. A distal end of the aspiration lumen 832typically ends proximal of the return electrode 806 while the distal endof the fluid delivery lumen 834 extends to a point adjacent the distalend of the electrosurgical probe 800. As shown in FIG. 41, the fluiddelivery lumen 834 preferably occupies a larger portion of the annularregion. In one specific embodiment, the fluid delivery lumen 834occupies approximately two-thirds of the annular region.

[0213] The electrosurgical probe may have a single active electrode 804or an electrode array distributed over a contact surface of a probe. Inthe latter embodiment, the electrode array usually includes a pluralityof independently current-limited and/or power-controlled activeelectrodes to apply electrical energy selectively to the target tissuewhile limiting the unwanted application of electrical energy to thesurrounding tissue and environment. In one specific configuration theelectrosurgical probe comprises 23 active electrodes. Of course, it willbe appreciated that the number, size, and configuration of the activeelectrodes may vary depending on the specific use of the electrosurgicalprobe (e.g. tissue contraction, tissue ablation, or the like).

[0214] The shaft 802 will usually house a plurality of wires or otherconductive elements axially therethrough to permit connection of activeelectrodes or electrode array 804 to a connector at the proximal end ofthe shaft (not shown). Each active electrode of an active electrodearray may be connected to a separate power source that is isolated fromthe other active electrodes. Alternatively, active electrodes 804 may beconnected to each other at either the proximal or distal ends of theprobe to form a single wire that couples to a power source.

[0215] The active electrode(s) 804 are typically supported by anelectrically insulating electrode support member 836 that extends fromthe electrosurgical probe 800. Electrode support member 836 typicallyextends from the distal end of shaft 802 about 1 mm to 20 mm. Electrodesupport member 836 typically comprises an insulating material (e.g., asilicone, ceramic, or glass material, such as alumina, zirconia and thelike) which could be formed at the time of manufacture in a flat,hemispherical or other shape according to the requirements of aparticular procedure.

[0216] In use, the electrosurgical probe 800 can be positioned adjacentthe target tissue, as described above. When treating an intervertebraldisc, the distal end of shaft 802 is typically delivered through theannulus to the nucleus pulposus 291, which may be herniated, extruded,non-extruded, or simply swollen. As shown in FIG. 42, high frequencyvoltage is applied between active electrode(s) 804 and returnelectrode(s) 806 to heat the surrounding collagen to suitabletemperatures for contraction (i.e., typically about 55° C. to about 70°C.) or ablation (i.e. typically less than 150° C.). As discussed above,this procedure may also be performed with a monopolar configuration.However, applicant has found that the bipolar configuration providesenhanced control of the high frequency current, which reduces the riskof spinal nerve damage.

[0217] In the exemplary embodiments, an electrically conductive fluid830 is delivered through fluid delivery lumen 834 to the target site. Inthese embodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to vaporize the electrically conductive fluid(e.g., gel or saline) between the active electrode(s) and the tissue.Within the vaporized fluid, an ionized plasma is formed and chargedparticles (e.g., electrons) are accelerated towards the tissue to causethe molecular breakdown or disintegration of several cell layers of thetissue. This molecular dissociation is accompanied by the volumetricremoval of the tissue. Because the aspiration lumen 832 is placedproximal of the return electrode (and typically outside of theintervertebral disc 290), the aspiration lumen 832 typically removes theair bubbles from the spinal disc and leaves the disc tissue relativelyintact. Moreover, because the aspiration lumen 834 is spaced from thetarget area, the conductive fluid 830 is allowed to stay in the targetarea longer and the plasma can be created more aggressively.

[0218]FIGS. 43A to 43D show embodiments of the electrosurgical probe ofthe present invention which have a curved or steerable distal tip forimproving navigation of the electrosurgical probe 800 within the disc.Referring now to FIG. 43A, probe 800 comprises an electricallyconductive shaft 802, a handle 803 coupled to the proximal end of shaft802 and an electrically insulating support member 836 at the distal endof shaft 802. Probe 800 further includes an insulating sleeve 838 overshaft 802, and an exposed portion of shaft 802 that functions as thereturn electrode 806. In the representative embodiment, probe 800comprises a plurality of active electrodes 804 extending from the distalend of support member 836. As shown, return electrode 806 is spaced afurther distance from active electrodes 804 than in the embodimentsdescribed above. In this embodiment, the return electrode 806 is spaceda distance of about 2.0 mm to 50 mm, preferably about 5 mm to 25 mm. Inaddition, return electrode 806 has a larger exposed surface area than inprevious embodiments, having a length in the range of about 2.0 mm to 40mm, preferably about 5 mm to 20 mm. Accordingly, electric currentpassing from active electrodes 804 to return electrode 806 will follow acurrent flow path 840 that is further away from shaft 802 than in theprevious embodiments. In some applications, this current flow path 840results in a deeper current penetration into the surrounding tissue withthe same voltage level, and thus increased thermal heating of thetissue. As discussed above, this increased thermal heating may haveadvantages in some applications of treating disc or other spinaldefects. Typically, it is desired to achieve a tissue temperature in therange of about 60° C. to 100° C. to a depth of about 0.2 mm to 5 mm,usually about 1 mm to 2 mm. The voltage required for this thermaltreatment will depend in part on the electrode configuration, theconductivity of the tissue and of the milieu immediately surrounding theelectrodes, and the time period during which the voltage is applied.With the electrode configuration described in FIGS. 43A-43D, the voltagelevel for thermal heating will usually be in the range of about 20 voltsrms to 300 volts rms, preferably about 60 volts rms to 200 volts rms.The peak-to-peak voltages for thermal heating with a square wave formhaving a crest factor of about 2 are typically in the range of about 40to 600 volts peak-to-peak, preferably about 120 to 400 voltspeak-to-peak. The higher the voltage is within this range, the less timerequired for a given effect. If the voltage is too high, however, thesurface tissue may be vaporized, debulked or ablated, which is oftenundesirable.

[0219] As shown by the dotted lines in FIGS. 43A-43D, the distal tip 837of the electrosurgical probe 800 can have a pre-formed curvature or canbe steered to a curved configuration so as to approximate the curvatureof the inner surface 839 of the annulus (FIGS. 46A-B). In someembodiments, distal tip 837 is made of a shape memory material that canbe shaped to approximate the inside curvature of the annulus. In otherembodiments, distal tip 837 of the electrosurgical probe 800 issteerable or deflectable by the user. The flexible shaft and steerabledistal tip may be combined with pull wires, shape memory actuators, heatactuated materials, or other conventional or proprietary mechanisms foreffecting selective deflection of the distal tip of the shaft tofacilitate positioning of the electrode array relative to a targettissue. A user can track the position of the steerable distal tip usingfluoroscopy, optical fibers, transducers positioned on the probe, or thelike.

[0220] In some embodiments, the electrosurgical probe 800 may include adispersive return electrode 842 (FIG. 44) for operating the apparatus inmonopolar mode. In this embodiment, the power supply 28 will typicallyinclude a switch, e.g., a foot pedal 843, for switching between themonopolar and bipolar modes. The system will switch between an ablationmode, where the dispersive pad 842 is deactivated and voltage is appliedbetween active and return electrodes 804, 806, and a subablation orthermal heating mode, where the active electrode(s) 804 are deactivatedand voltage is applied between the dispersive pad 842 and the returnelectrode 806. In the subablation mode, a lower voltage is typicallyapplied and the return electrode 806 functions as the active electrodeto provide thermal heating and/or coagulation of tissue surroundingreturn electrode 806. A more complete description of the use of thedispersive return electrode is described in co-pending U.S. patentapplication Ser. No. 09/316,472, filed May 21, 1999, the completedisclosure of which is incorporated herein by reference.

[0221]FIG. 43B illustrates yet another embodiment of the presentinvention. As shown, electrosurgical probe 800 comprises an electrodeassembly having one or more active electrode(s) 804 and a proximallyspaced return electrode 806 as in previous embodiments. Return electrode806 is typically spaced about 0.5 mm to 25 mm, preferably 1.0 mm to 5.0mm from the active electrode(s) 804, and has an exposed length of about1 mm to 20 mm. In addition, the electrode assembly can include twoadditional electrodes 844, 846 spaced axially on either side of returnelectrode 806. Electrodes 844, 846 are typically spaced about 0.5 mm to25 mm, preferably about 1 mm to 5 mm from return electrode 806. In therepresentative embodiment, the additional electrodes 844, 846 areexposed portions of shaft 802, and the return electrode 806 iselectrically insulated from shaft 802 such that a voltage difference maybe applied between electrodes 844, 846 and electrode 806. In thisembodiment, probe 800 may be used in at least two different modes, anablation mode and a subablation or thermal heating mode. In the ablationmode, voltage is applied between active electrode(s) 804 and returnelectrode 806 in the presence of electrically conductive fluid, asdescribed above. In the ablation mode, electrodes 844, 846 aredeactivated. In the thermal heating or coagulation mode, activeelectrode(s) 804 are deactivated and a voltage difference is appliedbetween electrodes 844, 846 and electrode 806 such that a high frequencycurrent 840 flows therebetween, as shown in FIG. 43B. In the thermalheating mode, a lower voltage is typically applied such that the voltageis below the threshold for plasma formation and ablation, but sufficientto cause some thermal damage to the tissue immediately surrounding theelectrodes without vaporizing or otherwise debulking this tissue so thatthe current 840 provides thermal heating and/or coagulation of tissuesurrounding electrodes 804, 844, 846.

[0222]FIG. 43C illustrates another embodiment of probe 800 incorporatingan electrode assembly having one or more active electrode(s) 804 and aproximally spaced return electrode 806 as in previous embodiments.Return electrode 806 is typically spaced about 0.5 mm to 25 mm,preferably 1.0 mm to 5.0 mm from the active electrode(s) 804, and has anexposed length of about 1 mm to 20 mm. In addition, the electrodeassembly includes a second active electrode 848 separated from returnelectrode 806 by an electrically insulating spacer 382. In thisembodiment, handle 803 includes a switch 850 for toggling probe 800between at least two different modes, an ablation mode and a subablationor thermal heating mode. In the ablation mode, voltage is appliedbetween active electrode(s) 804 and return electrode 806 in the presenceof electrically conductive fluid, as described above. In the ablationmode, electrode 848 is deactivated. In the thermal heating orcoagulation mode, active electrode(s) 804 may be deactivated and avoltage difference is applied between electrode 848 and electrode 806such that a high frequency current 840 flows therebetween.Alternatively, active electrode(s) 804 may not be deactivated as thehigher resistance of the smaller electrodes (active electrodes 804) mayautomatically send the electric current to electrode 848 without havingto physically decouple electrode(s) 804 from the circuit. In the thermalheating mode, a lower voltage is typically applied, i.e. a voltage belowthe threshold for plasma formation and ablation, but sufficient to causesome thermal damage to the tissue immediately surrounding the electrodeswithout vaporizing or otherwise debulking this tissue so that thecurrent 840 provides thermal heating and/or coagulation of tissuesurrounding electrodes 804, 848.

[0223]FIG. 43D illustrates yet another embodiment of the inventiondesigned for channeling through tissue and creating lesions therein totreat the interior tissue of intervertebral discs. As shown, probe 800is similar to the probe in FIG. 43C having a return electrode 806 and athird, coagulation electrode 848 spaced proximally from the returnelectrode 806. In this embodiment, active electrode 804 comprises asingle electrode wire extending distally from insulating support member836. Of course, the active electrode 804 may have a variety ofconfigurations to increase the current densities on its surfaces, e.g.,a conical shape tapering to a distal point, a hollow cylinder, loopelectrode and the like. This embodiment includes a proximal supportmember 852. In the representative embodiment, support members 836 and852 are constructed of inorganic material, such as a ceramic, a glass, asilicone, and the like. The proximal support member 852 may alsocomprise a more conventional organic material as this support member 852will generally not be in the presence of a plasma that would otherwiseetch or wear away an organic material.

[0224] The probe 800 in FIG. 43D does not include a switching element.In this embodiment, all three electrodes are activated when the powersupply is activated. The return electrode 806 has an opposite polarityfrom the active and coagulation electrodes 804, 848 such that current840 flows from the latter electrodes to the return electrode 806 asshown. In the preferred embodiment, the electrosurgical system includesa voltage reduction element or a voltage reduction circuit for reducingthe voltage applied between the coagulation electrode 848 and returnelectrode 806. The voltage reduction element allows the power supply 28(FIG. 1) to, in effect, apply two different voltages simultaneously totwo different electrodes. Thus, for channeling through tissue, theoperator may apply a voltage sufficient to provide ablation of thetissue at the tip of the probe (i.e., tissue adjacent to the activeelectrode 804). At the same time, the voltage applied to the coagulationelectrode 848 will be insufficient to ablate tissue. For thermal heatingor coagulation of tissue, for example, the voltage reduction elementwill serve to reduce a voltage from about 100 to 300 volts rms down toabout 45 to 90 volts rms, wherein the latter range provides a suitablevoltage for coagulation of tissue without ablation (e.g., withoutmolecular dissociation) of the tissue.

[0225] In the representative embodiment, the voltage reduction elementis a capacitor (not shown) coupled to the power supply and coagulationelectrode 848. The capacitor usually has a capacitance of about 200 pFto 500 pF (at 500 volts) and preferably about 300 pF to 350 pF (at 500volts). Of course, the capacitor may be located in other places withinthe system, such as in, or distributed along the length of, the cable,the generator, the connector, etc. In addition, it will be recognizedthat other voltage reduction elements, such as diodes, transistors,inductors, resistors, capacitors or combinations thereof, may be used inconjunction with the present invention. For example, the probe 800 mayinclude a coded resistor (not shown) that is constructed to lower thevoltage applied between the return and coagulation electrodes 806, 848.In addition, electrical circuits may be employed for this purpose.

[0226] Of course, for some procedures, the probe will typically notrequire a voltage reduction element. Alternatively, the probe mayinclude a voltage increasing element or circuit, if desired.Alternatively or additionally, cable 22 (FIG. 1) that couples powersupply 28 to probe 800 may be used as a voltage reduction element. Thecable has an inherent capacitance that can be used to reduce the powersupply voltage if the cable is placed into the electrical circuitbetween the power supply, the active electrodes and the returnelectrode. In this embodiment, the cable 22 may be used alone, or incombination with one of the voltage reduction elements discussed above,e.g., a capacitor. Further, it should be noted that the presentinvention can be used with a power supply that is adapted to apply twodifferent voltages within the selected range for treatment of tissue. Inthis embodiment, a voltage reduction element or circuitry may not bedesired.

[0227] In use, the electrosurgical instruments of FIGS. 43A-43D can beused to treat the tissue within the disc 290. In particular, theelectrosurgical instrument 800 can be used to treat damaged discs (e.g.,herniated, bulging, fissured, protruding, or the like), denervateselected nerves embedded in the annulus, cauterize granulation tissuethat is ingrown into the annulus, seal fissures along the inner surfaceof the annulus, and the like. Preferably, the electrosurgical probe 800can achieve these results in a minimally destructive manner so as tomaintain the water content and tissue mass within the disc. Of course,the present invention can also be adapted to ablate tissue, to shrinktissue, to decrease the mass of tissue, or to reduce the water contentof the disc.

[0228] In preferred embodiments, the electrosurgical probe 800 minimizesablation of the nucleus pulposus 291 by moving along an inner surface ofthe annulus 292. Accordingly, after the distal tip of theelectrosurgical probe is inserted into the disc 290 (FIG. 45), thedistal tip 837 can be steered along the interface between the annulus292 and nucleus pulposus 291.

[0229] Referring now to FIG. 45, in some methods the physician positionsactive electrode 804 adjacent to the tissue surface to be treated (e.g.,an intervertebral disc). The power supply is activated to provide anablation voltage between active and return electrodes 804, 806 and acoagulation or thermal heating voltage between coagulation and returnelectrodes 806, 848. An electrically conductive fluid can then beprovided around active electrode 804, and in the junction between theactive and return electrodes 804, 806 to provide a current flow paththerebetween. This may be accomplished in a variety of manners, asdiscussed above. The active electrode 804 is then advanced through thespace left by the ablated tissue to form a channel in the disc. Duringablation, the electric current between the coagulation and returnelectrode is typically insufficient to cause any damage to the surfaceof the tissue as these electrodes pass through the tissue surface intothe channel created by active electrode 804. Once the physician hasformed the channel to the appropriate depth, he or she will ceaseadvancement of the active electrode, and will either hold the instrumentin place for approximately 5 seconds to 30 seconds, or can immediatelyremove the distal tip of the instrument from the channel (see detaileddiscussion of this below). In either event, when the active electrode isno longer advancing, it will eventually stop ablating tissue.

[0230] Prior to entering the channel formed by the active electrode 804,an open circuit exists between return and coagulation electrodes 806,848. Once coagulation electrode 848 enters this channel, electriccurrent will flow from coagulation electrode 848, through the tissuesurrounding the channel, to return electrode 806. This electric currentwill heat the tissue immediately surrounding the channel to coagulateany severed vessels at the surface of the channel. If the physiciandesires, the instrument may be held within the channel for a period oftime to create a lesion around the channel.

[0231] In an exemplary embodiment, once the distal tip 837 of theelectrosurgical probe 800 has channeled through the annulus fibrosus292, the distal tip 837 can be steered or deflected so as to move alongthe inner surface of the annulus fibrosus 292. As shown in FIGS. 46A and46B, the electrosurgical device is advanced into an intervertebral disc290, and the physician can simultaneously steer the distal tip 237 fromthe proximal end of the electrosurgical device (not shown). As notedabove, the distal end of the electrosurgical device preferably issteered or deflected around the inner surface 839 of the annulusfibrosus 292. The physician can use fluoroscopy to monitor the positionand movement of the distal end of the probe. Alternatively, the surgeonmay insert an imaging device or transducer directly into the disc tomonitor the position of electrodes 804, 806, and 848. The imaging device(not shown) can be positioned on the electrosurgical probe or it can beon a separate instrument.

[0232] In other embodiments, instead of a steerable distal tip 837, thedistal tip of the electrosurgical probe 800 can be composed of ashape-memory material that can be pre-shaped to have the approximatecurve of the inner surface of the annulus 292. The shape-memory tip canbe biased to a pre-bent curved configuration, such that in the absenceof a straightening force (e.g., within the annulus, within a tube, orthe like) the distal tip will bias to the curved configuration. Forexample, after an operating corridor has been created to the targetsite, electrosurgical probe 800 can be moved adjacent the outer surfaceof the annulus fibrosus 292 (FIGS. 12-15). The active electrode 804 canchannel through the tough annulus fibrosus 292, as described above. Oncethe distal tip 837 enters the nucleus pulposus 291, the distal tip willno longer be constrained in the substantially straight configuration bythe tough, annulus fibrosus 292 and the distal tip will bias to itspre-bent curved configuration. As the electrosurgical device is advancedinto the disc 290, the biased distal tip encourages the electrosurgicalinstrument to follow the curved inner surface 839 of the annulusfibrosus 292.

[0233] As described in detail above, once electrosurgical probe 800 hasbeen steered to the target position, the high frequency voltage can bedelivered between the active electrode(s) and return electrode(s) in abipolar mode or monopolar mode to treat inner surface 839 of annulusfibrosus 292. In some embodiments, an electrically conductive fluid,such as isotonic saline, can be delivered to the active electrode. Asnoted above, in procedures requiring ablation of tissue, the tissue isremoved by molecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to vaporize the electrically conductive fluidbetween the active electrode(s) and the tissue. Within the vaporizedfluid, an ionized plasma is formed and charged particles (e.g.,electrons) cause the molecular breakdown or disintegration of the tissueto a depth of perhaps several cell layers. This molecular dissociationis accompanied by the volumetric removal of the tissue. The moleculardissociation process can be precisely controlled to target specifictissue structures or layers, thereby minimizing damage and necrosis tonon-target tissue. In monopolar embodiments, the conductive fluid needonly be sufficient to surround the active electrode and to provide alayer of fluid between the active electrode and the tissue. In bipolarembodiments, the conductive fluid preferably generates a current flowpath between the active electrode(s) and the return electrode(s).

[0234] Depending on the procedure, the inner surface 839 of annulus 292can be ablated, contracted, coagulated, sealed, or the like. Forexample, the high frequency voltage can be used to denervate the painreceptors in a fissure in the annulus fibrosus, deactivate theneurotransmitters, deactivate heat-sensitive enzymes, denervate nervesembedded in the wall of the annulus fibrosus, ablate granulation tissuein the annulus fibrosus, shrink collagen in the annulus fibrosus, or thelike.

[0235] Other modifications and variations can be made to discloseembodiments without departing from the subject invention as defined inthe following claims. For example, it should be noted that the inventionis not limited to an electrode array comprising a plurality of activeelectrodes. Certain embodiments of the invention could utilize aplurality of return electrodes, e.g., in a bipolar array or the like. Inaddition, depending on other conditions, such as the peak-to-peakvoltage, electrode diameter, etc., a single active electrode may besufficient to contract collagen tissue, ablate tissue, or the like.

[0236] In addition, the active and return electrodes may both be locatedon a distal tissue treatment surface adjacent to each other. The activeand return electrodes may be located in active/return electrode pairs,or one or more return electrodes may be located on the distal tiptogether with a plurality of electrically isolated active electrodes.The proximal return electrode may or may not be employed in theseembodiments. For example, if it is desired to maintain the current fluxlines around the distal tip of the probe, the proximal return electrodewill not be desired.

[0237] There now follows a description, with reference to FIGS. 47A-50B,of an electrosurgical probe having a curved shaft, according toadditional embodiments of the invention. FIG. 47A is a side view of anelectrosurgical probe 900, including a shaft 902 having a distal endportion 902 a and a proximal end portion 902 b. An active electrode 910is disposed on distal end portion 902 a. Although only one activeelectrode is shown in FIG. 26A, embodiments having a plurality of activeelectrodes are also within the scope of the invention. Probe 900 furtherincludes a handle 904 which houses a connection block 906 for couplingelectrodes, e.g. active electrode 910, thereto. Connection block 906includes a plurality of pins 908 adapted for coupling probe 900 to apower supply unit, e.g. power supply 28 (FIG. 1). FIG. 47A also shows afirst curve 924 and a second curve 926 located at shaft distal endportion 902 a, wherein second curve 926 is proximal to first curve 924.First curve 924 and second curve 926 may be separated by a linear (i.e.straight, or non-curved), or substantially linear, inter-curve portion925 of shaft 902.

[0238]FIG. 47B is a side view of shaft distal end portion 902 a within arepresentative introducer device or needle 928 having an inner diameterD. Shaft distal end portion 902 a includes first curve 924 and secondcurve 926 separated by inter-curve portion 925. In one embodiment, shaftdistal end portion 902a includes a linear or substantially linearproximal portion 901 extending from proximal end portion 902 b to secondcurve 926, a linear or substantially linear inter-curve portion 925between first and second curves 924, 926, and a linear or substantiallylinear distal portion 909 between first curve 924 and the distal tip ofshaft 902 (the distal tip is represented in FIG. 47B as an electrodehead 911). When shaft distal end portion 902 a is located withinintroducer needle 928, first curve 924 subtends a first angle ∀ to theinner surface of needle 928, and second curve 926 subtends a secondangle ∃ to inner surface 932 of needle 928. (In the situation shown inFIG. 47B, needle inner surface 932 is essentially parallel to thelongitudinal axis of shaft proximal end portion 902 b (FIG. 47A).) Inone embodiment, shaft distal end portion 902 a is designed such that theshaft distal tip occupies a substantially central transverse locationwithin the lumen of introducer needle 928 when shaft distal end portion902 a is translated axially with respect to introducer needle 928. Thus,as shaft distal end portion 902 a is advanced through the distal openingof needle 928 (FIGS. 30B, 31B), and then retracted back into the distalopening, the shaft distal tip will always occupy a transverse locationtowards the center of introducer needle 928 (even though the tip may becurved or biased away from the longitudinal axis of shaft 902 and needle928 upon its advancement past the distal opening of introducer needle928). In one embodiment, shaft distal end portion 902 a is flexible andhas a configuration which requires shaft distal end portion 902 a bedistorted in the region of at least second curve 926 by application of alateral force imposed by inner wall 932 of introducer needle 928 asshaft distal end portion 902 a is introduced or retracted into needle928. In one embodiment, first curve 924 and second curve 926 are in thesame plane relative to the longitudinal axis of shaft 902, and first andsecond curves 924, 926 are in opposite directions.

[0239] The “S-curve” configuration of shaft 902 shown in FIGS. 47A-Callows the distal end or tip of a device to be advanced or retractedthrough needle distal end 928 a and within the lumen of needle 928without the distal end or tip contacting introducer needle 928.Accordingly, this design allows a sensitive or delicate component to belocated at the distal tip of a device, wherein the distal end or tip isadvanced or retracted through a lumen of an introducer instrumentcomprising a relatively hard material (e.g., an introducer needlecomprising stainless steel). This design also allows a component locatedat a distal end or tip of a device to be constructed from a relativelysoft material, and for the component located at the distal end or tip tobe passed through an introducer instrument comprising a hard materialwithout risking damage to the component comprising a relatively softmaterial.

[0240] The “S-curve” design of shaft distal end portion 902 a allows thedistal tip (e.g., electrode head 911) to be advanced and retractedthrough the distal opening of needle 928 while avoiding contact betweenthe distal tip and the edges of the distal opening of needle 928. (If,for example, shaft distal end portion 902 a included only a singlecurve, the distal tip would ordinarily come into contact with needledistal end 928 a as shaft 902 is retracted into the lumen of needle928.) In preferred embodiments, the length L2 of distal portion 909 andthe angle ∀ between distal portion 909 and needle inner surface 932 928,when shaft distal end portion 902 a is compressed within needle 928, areselected such that the distal tip is substantially in the center of thelumen of needle 928, as shown in FIG. 47B. Thus, as the length L2increases, the angle ∀ will decrease, and vice versa. The exact valuesof length L2 and angle ∀ will depend on the inner diameter, D of needle928, the inner diameter, d of shaft distal end portion 902 a, and thesize of the shaft distal tip.

[0241] The presence of first and second curves, 924, 926 provides apre-defined bias in shaft 902. In addition, in one embodiment shaftdistal end portion 902 a is designed such that at least one of first andsecond curves 924, 926 are compressed to some extent as shaft distal endportion 902 a is retracted into the lumen of needle 928. Accordingly,the angle of at least one of curves 924, 926 may be changed when distalend portion 902 a is advanced out through the distal opening ofintroducer needle 928, as compared with the corresponding angle whenshaft distal end portion is completely retracted within introducerneedle 928. For example, FIG. 47C shows shaft 902 of FIG. 47B free fromintroducer needle 928, wherein first and second curves 924, 926 areallowed to adopt their natural or uncompressed angles ∀′ and ∃′,respectively, wherein ∃′ is typically equal to or greater than ∃. Angle∀′ may be greater than, equal to, or less than angle ∀. Angle ∃′ issubtended by inter-curve portion 925 and proximal portion 901. Whenshaft distal end portion 902 a is unrestrained by introducer needle 928,proximal portion 901 approximates the longitudinal axis of shaft 902.Angle ∀′ is subtended between linear distal portion 909 and a line drawnparallel to proximal portion 901. Electrode head 911 is omitted fromFIG. 47C for the sake of clarity.

[0242] The principle described above with reference to shaft 902 andintroducer needle 928 may equally apply to a range of other medicaldevices. That is to say, the “S-curve” configuration of the inventionmay be included as a feature of any medical system or apparatus in whicha medical instrument may be axially translated or passed within anintroducer device. In particular, the principle of the “S-curve”configuration of the invention may be applied to any apparatus whereinit is desired that the distal end of the medical instrument does notcontact or impinge upon the introducer device as the medical instrumentis advanced from or retracted into the introducer device. The introducerdevice may be any apparatus through which a medical instrument ispassed. Such medical systems may include, for example, a catheter, acannula, an endoscope, and the like.

[0243] When shaft 902 is advanced distally through the needle lumen to apoint where second curve 926 is located distal to needle distal end 928a, the shaft distal tip is deflected from the longitudinal axis ofneedle 928. The amount of this deflection is determined by the relativesize of angles ∃′ and ∀′, and the relative lengths of L1 and L2. Theamount of this deflection will in turn determine the size of a channelor lesion (depending on the application) formed in a tissue treated byelectrode head 911 when shaft 902 is rotated circumferentially withrespect to the longitudinal axis of probe 900.

[0244] As a result of the pre-defined bias in shaft 902, shaft distalend portion 902a will contact a larger volume of tissue than a linearshaft having the same dimensions. In addition, in one embodiment thepre-defined bias of shaft 902 allows the physician to guide or steer thedistal tip of shaft 902 by a combination of axial movement of needledistal end 928 a and the inherent curvature at shaft distal end portion902 a of probe 900.

[0245] Shaft 902 preferably has a length in the range of from about 4 to30 cm. In one aspect of the invention, probe 900 is manufactured in arange of sizes having different lengths and/or diameters of shaft 902. Ashaft of appropriate size can then be selected by the surgeon accordingto the body structure or tissue to be treated and the age or size of thepatient. In this way, patients varying in size from small children tolarge adults can be accommodated. Similarly, for a patient of a givensize, a shaft of appropriate size can be selected by the surgeondepending on the organ or tissue to be treated, for example, whether anintervertebral disc to be treated is in the lumbar spine or the cervicalspine. For example, a shaft suitable for treatment of a disc of thecervical spine may be substantially smaller than a shaft for treatmentof a lumbar disc. For treatment of a lumbar disc in an adult, shaft 902is preferably in the range of from about 15 to 20 cm. For treatment of acervical disc, shaft 902 is preferably in the range of from about 4 toabout 15 cm.

[0246] The diameter of shaft 902 is preferably in the range of fromabout 0.5 to about 2.5 mm, and more preferably from about 1 to 1.5 mm.First curve 924 is characterized by a length L1, while second curve 926is characterized by a length L2 (FIG. 47B). Inter-curve portion 925 ischaracterized by a length L3, while shaft 902 extends distally fromfirst curve 924 a length L4. In one embodiment, L2 is greater than L1.Length L1 may be in the range of from about 0.5 to about 5 mm, while L2may be in the range of from about 1 to about 10 mm. Preferably, L3 andL4 are each in the range of from about 1 to 6 mm.

[0247]FIG. 48A is a side view of electrosurgical probe 900 showingdetails of shaft distal end portion 902 a including an active electrodehead 911 of active electrode 910 (the latter not shown in FIG. 48A),according to one embodiment of the invention. Distal end portion 902 aincludes an insulating collar or spacer 916 proximal to active electrodehead 911, and a return electrode 918 proximal to collar 916. A firstinsulating sleeve (FIG. 48B) may be located beneath return electrode918. A second insulating jacket or sleeve 920 may extend proximally fromreturn electrode 918. Second insulating sleeve 920 serves as anelectrical insulator to inhibit current flow into non-target tissue. Ina currently preferred embodiment, probe 900 further includes a shield922 extending proximally from second insulating sleeve 920. Shield 922may be formed from a conductive metal such as stainless steel, and thelike. Shield 922 functions to decrease the amount of leakage currentpassing from probe 900 to a patient or a user (e.g., surgeon). Inparticular, shield 922 decreases the amount of capacitive couplingbetween return electrode 918 and an introducer needle 928 (FIG. 50A).

[0248] In this embodiment, electrode head 911 includes an apical spike911 a and an equatorial cusp 911 b. Electrode head 911 exhibits a numberof advantages as compared with, for example, an electrosurgical probehaving a blunt, globular, or substantially spherical active electrode.In particular, electrode head 911 provides a high current density atapical spike 911 a and cusp 911 b. In turn, high current density in thevicinity of an active electrode is advantageous in the generation of aplasma; and, as is described fully hereinabove, generation of a plasmain the vicinity of an active electrode is fundamental to ablation oftissue with minimal collateral thermal damage according to certainembodiments of the instant invention. Electrode head 911 provides anadditional advantage, in that the sharp edges of cusp 911 b, and moreparticularly of apical spike 911 a, facilitate movement and guiding ofhead 911 into fresh tissue during surgical procedures, as describedfully hereinbelow. In contrast, an electrosurgical probe having a bluntor rounded apical electrode is more likely to follow a path of leastresistance, such as a channel which was previously ablated withinnucleus pulposus tissue. Although certain embodiments of the inventiondepict head 911 as having a single apical spike, other shapes for theapical portion of active electrode 910 are also within the scope of theinvention.

[0249]FIG. 48B is a longitudinal cross-sectional view of distal endportion 902 a of shaft 902. Apical electrode head 911 is incommunication with a filament 912. Filament 912 typically comprises anelectrically conductive wire encased within a first insulating sleeve914. First insulating sleeve 914 comprises an insulator, such as varioussynthetic polymeric materials. An exemplary material from which firstinsulating sleeve 914 may be constructed is a polyimide. Firstinsulating sleeve 914 may extend the entire length of shaft 902 proximalto head 911. An insulating collar or spacer 916 is disposed on thedistal end of first insulating sleeve 914, adjacent to electrode head911. Collar 916 preferably comprises a material such as a glass, aceramic, or silicone. The exposed portion of first insulating sleeve 914(i.e., the portion proximal to collar 916) is encased within acylindrical return electrode 918. Return electrode 918 may extendproximally the entire length of shaft 902. Return electrode 918 maycomprise an electrically conductive material such as stainless steel,tungsten, platinum or its alloys, titanium or its alloys, molybdenum orits alloys, nickel or its alloys, and the like. A proximal portion ofreturn electrode 918 is encased within a second insulating sleeve 920,so as to provide an exposed band of return electrode 918 located distalto second sleeve 920 and proximal to collar 916. Second sleeve 920provides an insulated portion of shaft 920 which facilitates handling ofprobe 900 by the surgeon during a surgical procedure. A proximal portionof second sleeve 920 is encased within an electrically conductive shield922. Second sleeve 920 and shield 922 may also extend proximally for theentire length of shaft 902.

[0250]FIG. 49A shows distal end portion 902 a of shaft 902 extendeddistally from an introducer needle 928, according to one embodiment ofthe invention. Introducer needle 928 may be used to convenientlyintroduce shaft 902 into tissue, such as the nucleus pulposus of anintervertebral disc. In this embodiment, due to the curvature of shaftdistal end 902 a, when shaft 902 is extended distally beyond introducerneedle 928, head 911 is displaced laterally from the longitudinal axisof introducer needle 928. However, as shown in FIG. 49B, as shaft 902 isretracted into introducer needle 928, head 911 assumes a substantiallycentral transverse location within lumen 930 (see also FIG. 50B) ofintroducer 928. Such re-alignment of head 911 with the longitudinal axisof introducer 928 is achieved by specific design of the curvature ofshaft distal end 902 a, as accomplished by the instant inventors. Inthis manner, contact of various components of shaft distal end 902 a(e.g., electrode head 911, collar 916, return electrode 918) isprevented, thereby not only facilitating extension and retraction ofshaft 902 within introducer 928, but also avoiding a potential source ofdamage to sensitive components of shaft 902.

[0251]FIG. 50A shows a side view of shaft 902 in relation to an innerwall 932 of introducer needle 928 upon extension or retraction ofelectrode head 911 from, or within, introducer needle 928. Shaft 902 islocated within introducer 928 with head 911 adjacent to introducerdistal end 928 a (FIG. 50B). Under these circumstances, curvature ofshaft 902 may cause shaft distal end 902 a to be forced into contactwith introducer inner wall 932, e.g., at a location of second curve 926.Nevertheless, due to the overall curvature of shaft 902, and inparticular the nature and position of first curve 924 (FIGS. 47A-B),head 911 does not contact introducer distal end 928 a.

[0252]FIG. 50B shows an end view of electrode head 911 in relation tointroducer needle 928 at a point during extension or retraction of shaft902, wherein head 911 is adjacent to introducer distal end 928 a (FIGS.49B, 50B). In this situation, head 911 occupies a substantially centraltransverse location within lumen 930 of introducer 928. Therefore,contact between head 911 and introducer 928 is avoided, allowing shaftdistal end 902 a to be extended and retracted repeatedly withoutsustaining any damage to shaft 902.

[0253]FIG. 51A shows shaft proximal end portion 902 b of electrosurgicalprobe 900, wherein shaft 902 includes a plurality of depth markings 903(shown as 903 a-f in FIG. 51A). In other embodiments, other numbers andarrangements of depth markings 903 may be included on shaft 902. Forexample, in certain embodiments, depth markings may be present along theentire length of shield 922, or a single depth marking 903 may bepresent at shaft proximal end portion 902 b. Depth markings serve toindicate to the surgeon the depth of penetration of shaft 902 into apatient's tissue, organ, or body, during a surgical procedure. Depthmarkings 903 may be formed directly in or on shield 922, and maycomprise the same material as shield 922. Alternatively, depth markings903 may be formed from a material other than that of shield 922. Forexample, depth markings may be formed from materials which have adifferent color and/or a different level of radiopacity, as comparedwith material of shield 922. For example, depth markings may comprise ametal, such as tungsten, gold, or platinum oxide (black), having a levelof radiopacity different from that of shield 922. Such depth markingsmay be visualized by the surgeon during a procedure performed underfluoroscopy. In one embodiment, the length of introducer needle 928 andshaft 902 are selected to limit the range of shaft distal end 902 abeyond the distal tip of introducer needle 928.

[0254]FIG. 51B shows a probe 900, wherein shaft 902 includes amechanical stop 905. Preferably, mechanical stop 905 is located at shaftproximal end portion 902 b. Mechanical stop 905 limits the distance towhich shaft distal end 902 a can be advanced through introducer 928 bymaking mechanical contact with a proximal end 928 b of introducer 928.Mechanical stop 905 may be a rigid material or structure affixed to, orintegral with, shaft 902. Mechanical stop 905 also serves to monitor thedepth or distance of advancement of shaft distal end 902 a throughintroducer 928, and the degree of penetration of distal end 902 a into apatient's tissue, organ, or body. In one embodiment, mechanical stop 905is movable on shaft 902, and stop 905 includes a stop adjustment unit907 for adjusting the position of stop 905 and for locking stop 905 at aselected location on shaft 902.

[0255]FIG. 52A schematically represents a normal intervertebral disc 290in relation to the spinal cord 818, the intervertebral disc having anouter annulus fibrosus 292 enclosing an inner nucleus pulposus 291. Thenucleus pulposus is a relatively soft tissue comprising proteins andhaving a relatively high water content, as compared with the harder,more fibrous annulus fibrosus. FIGS. 52B-D each schematically representan intervertebral disc having a disorder which can lead to discogenicpain, for example due to compression of a nerve root by a distortedannulus fibrosus. Thus, FIG. 52B schematically represents anintervertebral disc exhibiting a bulge or protrusion of the nucleuspulposus and a concomitant distortion of the annulus fibrosus. Thecondition depicted in FIG. 52B clearly represents a containedherniation, which can result in severe and often debilitating pain. FIG.52C schematically represents an intervertebral disc exhibiting aplurality of fissures 1106 within the annulus fibrosus, again withconcomitant distortion of the annulus fibrosus. Such annular fissuresmay be caused by excessive pressure exerted by the nucleus pulposus onthe annulus fibrosus. Excessive pressure within the nucleus pulposustends to intensify disc disorders associated with the presence of suchfissures. FIG. 52D schematically represents an intervertebral discexhibiting fragmentation of the nucleus pulposus and a concomitantdistortion of the annulus fibrosus. In this situation, over time, errantfragment 291′ of the nucleus pulposus tends to dehydrate and to diminishin size, often leading to a decrease in discogenic pain over an extendedperiod of time (e.g., several months). For the sake of clarity, eachFIGS. 52B, 52C, 52D shows a single disorder. However, in practice morethan one of the depicted disorders may occur in the same disc.

[0256] Many patients suffer from discogenic pain resulting, for example,from conditions of the type depicted in FIGS. 52B-D. However, only asmall percentage of such patients undergo laminotomy or discectomy.Presently, there is a need for interventional treatment for the largegroup of patients who ultimately do not undergo major spinal surgery,but who sustain significant disability due to various disorders ordefects of an intervertebral disc. A common disorder of intervertebraldiscs is a contained herniation in which the nucleus pulposus does notbreach the annulus fibrosus, but a protrusion of the disc causescompression of the exiting nerve root, leading to radicular pain.Typical symptoms are leg pain compatible with sciatica. Such radicularpain may be considered as a particular form of discogenic pain. Mostcommonly, contained herniations leading to radicular pain are associatedwith the lumbar spine, and in particular with intervertebral discs ateither L4-5 or L5-S1. Various disc defects are also encountered in thecervical spine. Methods and apparatus of the invention are applicable toall segments of the spine, including the cervical spine and the lumbarspine.

[0257]FIG. 53 schematically represents shaft 902 of probe 900 insertedwithin a nucleus pulposus of a disc having at least one fissure in theannulus. Shaft 902 may be conveniently inserted within the nucleuspulposus via introducer needle 928 in a minimally invasive percutaneousprocedure. In a preferred embodiment, a disc in the lumbar spine may beaccessed via a posterior lateral approach, although other approaches arepossible and are within the scope of the invention. The preferred lengthand diameter of shaft 902 and introducer needle 928 to be used in aprocedure will depend on a number of factors, including the region ofthe spine (e.g., lumbar, cervical) or other body region to be treated,and the size of the patient. Preferred ranges for shaft 902 are givenelsewhere herein. In one embodiment for treatment of a lumbar disc,introducer needle 928 preferably has a diameter in the range of fromabout 50% to 150% the internal diameter of a 17 Gauge needle. In anembodiment for treatment of a cervical disc, introducer needle 928preferably has a diameter in the range of from about 50% to 150% theinternal diameter of a 20 Gauge needle.

[0258] Shaft 902 includes an active electrode 910, as describedhereinabove. Shaft 902 features curvature at distal end 902 a/902′a, forexample, as described with reference to FIGS. 47A-B. By rotating shaft902 through approximately 180°, shaft distal end 902 a can be moved to aposition indicated by the dashed lines and labeled as 902′a. Thereafter,rotation of shaft 902 through an additional 180° defines a substantiallycylindrical three-dimensional space with a proximal frusto-conicalregion, the latter represented as a hatched area (shown between 902 aand 902′a). The bi-directional arrow distal to active electrode 910indicates translation of shaft 902 substantially along the longitudinalaxis of shaft 902. By a combination of axial and rotational movement ofshaft 902, a much larger volume of the nucleus pulposus can be contactedby electrode 910, as compared with a corresponding probe having a linear(non-curved) shaft. Furthermore, the curved nature of shaft 902 allowsthe surgeon to change the direction of advancement of shaft 902 byappropriate rotation thereof, and to guide shaft distal end 902 a to aparticular target site within the nucleus pulposus. In addition, furthercontrol may be exerted over which sites or regions within the disc canbe accessed by shaft distal end 902 a by advancing or retractingintroducer needle 928 to change the initiation point from which shaftdistal end 902 a may be guided or steered. Alternatively, selection ofan appropriate position from which shaft distal end 902 a may beadvanced, guided, or steered to a target location may make use of anintroducer extension tube (FIG. 61A) which acts as an extension ofintroducer needle 928. By changing the location of the introducer needleor the introducer extension tube relative to the disc, different regionsof the disc can be accessed by shaft distal end 902 a.

[0259] It is to be understood that according to certain embodiments ofthe invention, the curvature of shaft 902 is the same, or substantiallythe same, both prior to it being used in a surgical procedure and whileit is performing ablation during a procedure, e.g., within anintervertebral disc. (One apparent exception to this statement, relatesto the stage in a procedure wherein shaft 902 may be transiently“molded” into a somewhat more linear configuration by the constraints ofintroducer inner wall 932 during housing, or passing, of shaft 902within introducer 928.) In contrast, certain prior art devices, andembodiments of the invention to be described hereinbelow (e.g., withreference to FIGS. 59A, 59B), may be linear or lacking a naturallydefined configuration prior to use, and then be steered into a selectedconfiguration during a surgical procedure.

[0260] While shaft distal end 902 a is at or adjacent to a target sitewithin the nucleus pulposus, probe 900 may be used to ablate tissue byapplication of a first high frequency voltage between active electrode910 and return electrode 918 (e.g., FIG. 26B), wherein the volume of thenucleus pulposus is decreased, the pressure exerted by the nucleuspulposus on the annulus fibrosus is decreased, and at least one nerve ornerve root is decompressed. Accordingly, discogenic pain experienced bythe patient may be alleviated. Preferably, application of the first highfrequency voltage results in formation of a plasma in the vicinity ofactive electrode 910, and the plasma causes ablation by breaking downhigh molecular weight disc tissue components (e.g., proteins) into lowmolecular weight gaseous materials. Such low molecular weight gaseousmaterials may be at least partially vented or exhausted from the disc,e.g., by piston action, upon removal of shaft 902 and introducer 928from the disc and the clearance between introducer needle 928 and shaft902. In addition, by-products of tissue ablation may be removed by anaspiration device (not shown in FIG. 53), as is well known in the art.In this manner, the volume and/or mass of the nucleus pulposus may bedecreased.

[0261] In order to initiate and/or maintain a plasma in the vicinity ofactive electrode 910, a quantity of an electrically conductive fluid maybe applied to shaft 902 and/or the tissue to ablated. The electricallyconductive fluid may be applied to shaft 902 and/or to the tissue to beablated, either before or during application of the first high frequencyvoltage. Examples of electrically conductive fluids are saline (e.g.,isotonic saline), and an electrically conductive gel. An electricallyconductive fluid may be applied to the tissue to be ablated before orduring ablation. A fluid delivery unit or device may be a component ofthe electrosurgical probe itself, or may comprise a separate device,e.g., ancillary device 940 (FIG. 57). Alternatively, many body fluidsand/or tissues (e.g., the nucleus pulposus, blood) at the site to beablated are electrically conductive and can participate in initiation ormaintenance of a plasma in the vicinity of the active electrode.

[0262] In one embodiment, after ablation of nucleus pulposus tissue bythe application of the first high frequency voltage and formation of acavity or channel within the nucleus pulposus, a second high frequencyvoltage may be applied between active electrode 910 and return electrode918, wherein application of the second high frequency voltage causescoagulation of nucleus pulposus tissue adjacent to the cavity orchannel. Such coagulation of nucleus pulposus tissue may lead toincreased stiffness, strength, and/or rigidity within certain regions ofthe nucleus pulposus, concomitant with an alleviation of discogenicpain. Furthermore, coagulation of tissues may lead to necrotic tissuewhich is subsequently broken down as part of a natural bodily processand expelled from the body, thereby resulting in de-bulking of the disc.Although FIG. 53 depicts a disc having fissures within the annulusfibrosus, it is to be understood that apparatus and methods of theinvention discussed with reference to FIG. 53 are also applicable totreating other types of disc disorders, including those described withreference to FIGS. 52B, 52D.

[0263]FIG. 54 shows shaft 902 of electrosurgical probe 900 within anintervertebral disc, wherein shaft distal end 902 a is targeted to aspecific site within the disc. In the situation depicted in FIG. 54, thetarget site is occupied by an errant fragment 291′ of nucleus pulposustissue. Shaft distal end 902 may be guided or directed, at least inpart, by appropriate placement of introducer 928, such that activeelectrode 910 is in the vicinity of fragment 291′. Preferably, activeelectrode 910 is adjacent to, or in contact with, fragment 291′.Although FIG. 54 depicts a disc in which a fragment of nucleus pulposusis targeted by shaft 902, the invention described with reference to FIG.54 may also be used for targeting other aberrant structures within anintervertebral disc, including annular fissures and containedherniations. In a currently preferred embodiment, shaft 902 includes atleast one curve (not shown in FIG. 54), and other features describedherein with reference to FIGS. 26A-35, wherein shaft distal end 902 amay be precisely guided by an appropriate combination of axial androtational movement of shaft 902. The procedure illustrated in FIG. 54may be performed generally according to the description presented withreference to FIG. 53. That is, shaft 902 is introduced into the disc viaintroducer 928 in a percutaneous procedure. After shaft distal end 902 ahas been guided to a target site, tissue at or adjacent to that site isablated by application of a first high frequency voltage. Thereafter,depending on the particular condition of the disc being treated, asecond high frequency voltage may optionally be applied in order tolocally coagulate tissue within the disc.

[0264]FIG. 55 schematically represents a series of steps involved in amethod of ablating disc tissue according to the present invention;wherein step 1200 involves advancing an introducer needle towards anintervertebral disc to be treated. The introducer needle has a lumenhaving a diameter greater than the diameter of the shaft distal end,thereby allowing free passage of the shaft distal end through the lumenof the introducer needle. In one embodiment, the introducer needlepreferably has a length in the range of from about 3 cm to about 25 cm,and the lumen of the introducer needle preferably has a diameter in therange of from about 0.5 cm. to about 2.5 mm. Preferably, the diameter ofthe shaft distal end is from about 30% to about 95% of the diameter ofthe lumen. The introducer needle may be inserted in the intervertebraldisc percutaneously, e.g. via a posterior lateral approach. In oneembodiment, the introducer needle may have dimensions similar to thoseof an epidural needle, the latter well known in the art.

[0265] Optional step 1202 involves introducing an electricallyconductive fluid, such as saline, into the disc. In one embodiment, inlieu of step 1202, the ablation procedure may rely on the electricalconductivity of the nucleus pulposus itself. Step 1204 involvesinserting the shaft of the electrosurgical probe into the disc, e.g.,via the introducer needle, wherein the distal end portion of the shaftbears an active electrode and a return electrode. In one embodiment, theshaft includes an outer shield, first and second curves at the distalend portion of the shaft, and an electrode head having an apical spike,generally as described with reference to FIGS. 26A-32.

[0266] Step 1206 involves ablating at least a portion of disc tissue byapplication of a first high frequency voltage between the activeelectrode and the return electrode. In particular, ablation of nucleuspulposus tissue according to methods of the invention serves to decreasethe volume of the nucleus pulposus, thereby relieving pressure exertedon the annulus fibrosus, with concomitant decompression of a previouslycompressed nerve root, and alleviation of discogenic pain.

[0267] In one embodiment, the introducer needle is advanced towards theintervertebral disc until it penetrates the annulus fibrosus and entersthe nucleus pulposus. The shaft distal end in introduced into thenucleus pulposus, and a portion of the nucleus pulposus is ablated.These and other stages of the procedure may be performed underfluoroscopy to allow visualization of the relative location of theintroducer needle and shaft relative to the nucleus pulposus of thedisc. Additionally or alternatively, the surgeon may introduce theintroducer needle into the nucleus pulposus from a first side of thedisc, then advance the shaft distal end through the nucleus pulposusuntil resistance to axial translation of the electrosurgical probe isencountered by the surgeon. Such resistance may be interpreted by thesurgeon as the shaft distal end having contacted the annulus fibrosus atthe opposite side of the disc. Then, by use of depth markings on theshaft (FIG. 51A), the surgeon can retract the shaft a defined distancein order to position the shaft distal end at a desired location relativeto the nucleus pulposus. Once the shaft distal end is suitablypositioned, high frequency voltage may be applied to the probe via thepower supply unit.

[0268] After step 1206, optional step 1208 involves coagulating at leasta portion of the disc tissue. In one embodiment, step 1206 results inthe formation of a channel or cavity within the nucleus pulposus.Thereafter, tissue at the surface of the channel may be coagulatedduring step 1208. Coagulation of disc tissue may be performed byapplication of a second high frequency voltage, as describedhereinabove. After step 1206 or step 1208, the shaft may be moved (step1210) such that the shaft distal end contacts fresh tissue of thenucleus pulposus. The shaft may be axially translated (i.e. moved in thedirection of its longitudinal axis), may be rotated about itslongitudinal axis, or may be moved by a combination of axial androtational movement. In the latter case, a substantially spiral path isdefined by the shaft distal end. After step 1210, steps 1206 and 1208may be repeated with respect to the fresh tissue of the nucleus pulposuscontacted by the shaft distal end. Alternatively, after step 1206 orstep 1208, the shaft may be withdrawn from the disc (step 1212). Step1214 involves withdrawing the introducer needle from the disc. In oneembodiment, the shaft and the needle may be withdrawn from the discconcurrently. Withdrawal of the shaft from the disc may facilitateexhaustion of ablation by-products from the disc. Such ablationby-products include low molecular weight gaseous compounds derived frommolecular dissociation of disc tissue components, as describedhereinabove.

[0269] The above method may be used to treat any disc disorder in whichCoblation® and or coagulation of disc tissue is indicated, includingcontained herniations. In one embodiment, an introducer needle may beintroduced generally as described for step 1200, and a fluoroscopicfluid may be introduced through the lumen of the introducer needle forthe purpose of visualizing and diagnosing a disc defect or disorder.Thereafter, depending on the diagnosis, a treatment procedure may beperformed, e.g., according to steps 1202 through 1214, using the sameintroducer needle as access. In one embodiment, a distal portion, or theentire length, of the introducer needle may have an insulating coatingon its external surface. Such an insulating coating on the introducerneedle may prevent interference between the electrically conductiveintroducer needle and electrode(s) on the probe.

[0270] The size of the cavity or channel formed in a tissue by a singlestraight pass of the shaft through the tissue to be ablated is afunction of the diameter of the shaft (e.g., the diameter of the shaftdistal end and active electrode) and the amount of axial translation ofthe shaft. (By a “single straight pass” of the shaft is meant one axialtranslation of the shaft in a distal direction through the tissue, inthe absence of rotation of the shaft about the longitudinal axis of theshaft, with the power from the power supply turned on.) In the case of acurved shaft, according to various embodiments of the instant invention,a larger channel can be formed by rotating the shaft as it is advancedthrough the tissue. The size of a channel formed in a tissue by a singlerotational pass of the shaft through the tissue to be ablated is afunction of the deflection of the shaft, and the amount of rotation ofthe shaft about its longitudinal axis, as well as the diameter of theshaft (e.g., the diameter of the shaft distal end and active electrode)and the amount of axial translation of the shaft. (By a “singlerotational pass” of the shaft is meant one axial translation of theshaft in a distal direction through the tissue, in the presence ofrotation of the shaft about the longitudinal axis of the shaft, with thepower from the power supply turned on.) To a large extent, the diameterof a channel formed during a rotational pass of the shaft through tissuecan be controlled by the amount of rotation of the shaft, wherein the“amount of rotation” encompasses both the rate of rotation (e.g., theangular velocity of the shaft), and the number of degrees through whichthe shaft is rotated (e.g. the number of turns) per unit length of axialmovement. Typically, according to the invention, the amount of axialtranslation per pass (for either a straight pass or a rotational pass)is not limited by the length of the shaft. Instead, the amount of axialtranslation per single pass is preferably determined by the size of thetissue to be ablated. Depending on the size of the disc or other tissueto be treated, and the nature of the treatment, etc., a channel formedby a probe of the instant invention may preferably have a length in therange of from about 2 mm to about 50 mm, and a diameter in the range offrom about 0.5 mm to about 7.5 mm. In comparison, a channel formed by ashaft of the instant invention during a single rotational pass maypreferably have a diameter in the range of from about 1.5 mm to about 25mm.

[0271] A channel formed by a shaft of the instant invention during asingle straight pass may preferably have a volume in the range of fromabout 1 mm³, or less, to about 2,500 mm³. More preferably, a channelformed by a straight pass of a shaft of the instant invention has avolume in the range of from about 10 mm³ to about 2,500 mm³, and morepreferably in the range of from about 50 mm³ to about 2,500 mm³. Incomparison, a channel formed by a shaft of the instant invention duringa single rotational pass typically has a volume from about twice toabout 15 times the volume of a channel of the same length formed duringa single rotational pass, i.e., in the range of from about 2 mm³ toabout 4,000 mm³, more preferably in the range of from about 50 mm³ toabout 2,000 mm³. While not being bound by theory, the reduction involume of a disc having one or more channels therein is a function ofthe total volume of the one or more channels.

[0272]FIG. 56 schematically represents a series of steps involved in amethod of guiding the distal end of a shaft of an electrosurgical probeto a target site within an intervertebral disc for ablation ofspecifically targeted disc tissue, wherein steps 1300 and 1302 areanalogous to steps 1200 and 1204 of FIG. 55. Thereafter step 1304involves guiding the shaft distal end to a defined region within thedisc. The specific target site may be pre-defined as a result of aprevious procedure to visualize the disc and its defect, e.g., via X-rayexamination, endoscopically, or fluoroscopically. As an example, adefined target site within a disc may comprise a fragment of the nucleuspulposus that has migrated within the annulus fibrosus (see, e.g., FIG.52D) resulting in discogenic pain. However, guiding the shaft to definedsites associated with other types of disc disorders are also possibleand is within the scope of the invention. In one embodiment, as aprelude to guiding the shaft distal end to a target site, the shaftdistal end may first be introduced into the disc at a selected locationwithin the disc. Such a selected location defines a space within thedisc from where the shaft distal end may be advanced in order to reachor access the target site. Preferably, the selected location defines aspace in the general vicinity of the target site from where the shaftdistal end may readily access the target site. The shaft distal end maybe introduced at the selected location within the disc by advancing orretracting the introducer needle within the disc until the introducerneedle distal end reaches the selected location. In another embodiment,the shaft distal end may be introduced at the selected location withinthe disc by advancing or retracting an introducer extension tube withinthe lumen of the introducer needle until the distal end of theintroducer extension tube reaches the selected location (FIGS. 62A-B).

[0273] Guiding the shaft distal end to the defined target site may beperformed by axial and/or rotational movement of a curved shaft, asdescribed hereinabove. Or the shaft may be steerable, for example, bymeans of a guide wire, as is well known in the art. Guiding the shaftdistal end may be performed during visualization of the location of theshaft relative to the disc, wherein the visualization may be performedendoscopically or via fluoroscopy. Endoscopic examination may employ afiber optic cable (not shown). The fiber optic cable may be integralwith the electrosurgical probe, or be part of a separate instrument(endoscope). Step 1306 involves ablating disc tissue, and is analogousto step 1206 (FIG. 55). Before or during step 1306, an electricallyconductive fluid may be applied to the disc tissue and/or the shaft inorder to provide a path for current flow between active and returnelectrodes on the shaft, and to facilitate and/or maintain a plasma inthe vicinity of the distal end portion of the shaft. After the shaftdistal end has been guided to a target site and tissue at that site hasbeen ablated, the shaft may be moved locally, e.g., within the sameregion of the nucleus pulposus, or to a second defined target sitewithin the same disc. The shaft distal end may be moved as describedherein (e.g., with reference to step 1210, FIG. 55). Or, according to analternative embodiment, the shaft may be steerable, e.g., by techniqueswell known in the art. Steps 1310 and 1312 are analogous to steps 1212and 1214, respectively (described with reference to FIG. 55).

[0274] It is known in the art that epidural steroid injections cantransiently diminish perineural inflammation of an affected nerve root,leading to alleviation of discogenic pain. In one embodiment of theinvention, methods for ablation of disc tissue described hereinabove maybe conveniently performed in conjunction with an epidural steroidinjection. For example, ablation of disc tissue and epidural injectioncould be carried out as part of a single procedure, by the same surgeon,using equipment common to both procedures (e.g. visualizationequipment). Combining Coblation® and epidural injection in a singleprocedure may provide substantial cost-savings to the healthcareindustry, as well as a significant improvement in patient care.

[0275] As alluded to hereinabove, methods and apparatus of the presentinvention can be used to accelerate the healing process ofintervertebral discs having fissures and/or contained herniations. Inone method, the present invention is useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. For example, as described above in relation to FIGS.18-20, a percutaneous penetration can be made in the patient's back sothat the superior lamina can be accessed. Typically, a small needle isused initially to localize the disc space level, and a guide wire isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina. Sequential cannulated dilators can be inserted over theguide wire and each other to provide a hole from the incision to thelamina. The first dilator may be used to “palpate” the lamina, assuringproper location of its tip between the spinous process and facet complexjust above the inferior edge of the lamina. A tubular retractor can thenbe passed over the largest dilator down to the lamina. The dilators canthen be removed, so as to establish an operating corridor within thetubular retractor. It should be appreciated however, that otherconventional or proprietary methods can be used to access the targetintervertebral disc. Once the target intervertebral disc has beenaccessed, an introducer device may be inserted into the intervertebraldisc.

[0276] With reference to FIG. 57, in one embodiment, both introducerneedle 928 and a second or ancillary introducer 938 may be inserted intothe same disc, to allow introduction of an ancillary device 940 into thetarget disc via ancillary introducer 938. Ancillary device 940 maycomprise, for example, a fluid delivery device, a return electrode, anaspiration lumen, a second electrosurgical probe, or an endoscope havingan optical fiber component. Each of introducer needle 928 and ancillaryintroducer 938 may be advanced through the annulus fibrosus until atleast the distal end portion of each introducer 928 and 938, ispositioned within the nucleus pulposus. Thereafter, shaft 902″ ofelectrosurgical probe 900′ may be inserted through at least one ofintroducers 928, 938, to treat the intervertebral disc. Typically, shaft902″ of probe 900′ has an outer diameter no larger than about 7 French(1 Fr: 0.33 mm), and preferably between about 6 French and 7 French.

[0277] Prior to inserting electrosurgical probe 900 into theintervertebral disc, an electrically conductive fluid can be deliveredinto the disk via a fluid delivery assembly (e.g., ancillary device 940)in order to facilitate or promote the Coblation® mechanism within thedisc following the application of a high frequency voltage via probe900′. By providing a separate device (940) for fluid delivery, thedimensions of electrosurgical probe 900′ can be kept to a minimum.Furthermore, when the fluid delivery assembly is positioned withinancillary introducer 938, electrically conductive fluid can beconveniently replenished to the interior of the disc at any given timeduring the procedure. Nevertheless, in other embodiments, the fluiddelivery assembly can be physically coupled to electrosurgical probe900′.

[0278] In some methods, a radiopaque contrast solution (not shown) maybe delivered through a fluid delivery assembly so as to allow thesurgeon to visualize the intervertebral disc under fluoroscopy. In someconfigurations, a tracking device 942 can be positioned on shaft distalend portion 902″a. Additionally or alternatively, shaft 902″ can bemarked incrementally, e.g., with depth markings 903, to indicate to thesurgeon how far the active electrode is advanced into the intervertebraldisc. In one embodiment, tracking device 942 includes a radiopaquematerial that can be visualized under fluoroscopy. Such a trackingdevice 942 and depth markings 903 provide the surgeon with means totrack the position of the active electrode 910 relative to a specifictarget site within the disc to which active electrode 910 is to beguided. Such specific target sites may include, for example, an annularfissure, a contained herniation, or a fragment of nucleus pulposus. Thesurgeon can determine the position of the active electrode 910 byobserving the depth markings 903, or by comparing tracking deviceoutput, and a fluoroscopic image of the intervertebral disc to apre-operative fluoroscopic image of the target intervertebral disc.

[0279] In other embodiments, an optical fiber (not shown) can beintroduced into the disc. The optical fiber may be either integral withprobe 900′ or may be introduced as part of an ancillary device 940 viaancillary introducer 938. In this manner, the surgeon can visuallymonitor the interior of the intervertebral disc and the position ofactive electrode 910.

[0280] In addition to monitoring the position of the distal portion ofelectrosurgical probe 900′, the surgeon can also monitor whether theprobe is in Coblation® mode. In most embodiments, power supply 28 (e.g.,FIG. 1) includes a controller having an indicator, such as a light, anaudible sound, or a liquid crystal display (LCD), to indicate whetherprobe 900′ is generating a plasma within the disc. If it is determinedthat the Coblation® mechanism is not occurring, (e.g., due to aninsufficiency of electrically conductive fluid within the disc), thesurgeon can then replenish the supply of the electrically conductivefluid to the disc.

[0281]FIG. 58 is a side view of an electrosurgical probe 900′ includingshaft 902′ having tracking device 942 located at distal end portion902″a. Tracking device 942 may serve as a radiopaque marker adapted forguiding distal end portion 902″a within a disc. Shaft 902″ also includesat least one active electrode 910 disposed on the distal end portion902″a. Preferably, electrically insulating support member or collar 916is positioned proximal of active electrode 910 to insulate activeelectrode 910 from at least one return electrode 918. In mostembodiments, the return electrode 918 is positioned on the distal endportion of the shaft 902″ and proximal of the active electrode 910. Inother embodiments, however, return electrode 918 can be omitted fromshaft 902″, in which case at least one return electrode may be providedon ancillary device 940, or the return electrode may be positioned onthe patient's body, as a dispersive pad (not shown).

[0282] Although active electrode 910 is shown in FIG. 58 as comprising asingle apical electrode, other numbers, arrangements, and shapes foractive electrode 910 are within the scope of the invention. For example,active electrode 910 can include a plurality of isolated electrodes in avariety of shapes. Active electrode 910 will usually have a smallerexposed surface area than return electrode 918, such that the currentdensity is much higher at active electrode 910 than at return electrode918. Preferably, return electrode 918 has a relatively large, smoothsurfaces extending around shaft 902″ in order to reduce currentdensities in the vicinity of return electrode 918, thereby minimizingdamage to non-target tissue.

[0283] While bipolar delivery of a high frequency energy is thepreferred method of debulking the nucleus pulposus, it should beappreciated that other energy sources (i.e., resistive, or the like) canbe used, and the energy can be delivered with other methods (i.e.,monopolar, conductive, or the like) to debulk the nucleus.

[0284]FIG. 59A shows a steerable electrosurgical probe 950 including ashaft 952, according to another embodiment of the invention. Preferably,shaft 952 is flexible and may assume a substantially linearconfiguration as shown. Probe 950 includes handle 904, shaft distal end952 a, active electrode 910, insulating collar 916, and return electrode918. As can be seen in FIG. 59B, under certain circumstances, e.g., uponapplication of a force to shaft 952 during guiding or steering probe 950during a procedure, shaft distal end 952 a can adopt a non-linearconfiguration, designated 952′a. The deformable nature of shaft distalend 952′a allows active electrode 910 to be guided to a specific targetsite within a disc.

[0285]FIG. 60 shows steerable electrosurgical probe 950 inserted withinthe nucleus pulposus of an intervertebral disc. An ancillary device 940and ancillary introducer 928 may also be inserted within the nucleuspulposus of the same disc. To facilitate the debulking of the nucleuspulposus adjacent to a contained herniation, shaft 952 (FIG. 59A) can bemanipulated to a non-linear configuration, represented as 952′.Preferably, shaft 952/952′ is flexible over at least shaft distal end952 a so as to allow steering of active electrode 910 to a positionadjacent to the targeted disc defect. The flexible shaft may be combinedwith a sliding outer shield, a sliding outer introducer needle, pullwires, shape memory actuators, and other known mechanisms (not shown)for effecting selective deflection of distal end 952 a to facilitatepositioning of active electrode 910 within a disc. Thus, it can be seenthat the embodiment of FIG. 60 may be used for the targeted treatment ofannular fissures, or any other disc defect for which Coblation® isindicated.

[0286] In one embodiment shaft 952 has a suitable diameter and length toallow the surgeon to reach the target disc or vertebra by introducingthe shaft through the thoracic cavity, the abdomen or the like. Thus,shaft 952 may have a length in the range of from about 5.0 cm to 30.0cm, and a diameter in the range of about 0.2 mm to about 20 mm.Alternatively, shaft 952 may be delivered percutaneously in a posteriorlateral approach. Regardless of the approach, shaft 952 may beintroduced via a rigid or flexible endoscope. In addition, it should benoted that the methods described with reference to FIGS. 57 and 60 mayalso be performed in the absence of ancillary introducer 938 andancillary device 940.

[0287]FIG. 61A shows an electrosurgical apparatus or system including aprobe 1050 in combination with an introducer extension tube 1054,according to another aspect of the invention. Probe 1050 generallyincludes at least one active electrode 910 disposed at a shaft distalend 1502 a, an electrically insulating spacer or support 916 proximal toactive electrode 910, and a return electrode 918 proximal to support916. FIG. 61A shows shaft distal end 1502 a positioned within introducerextension tube 1054, which is in turn positioned within introducerneedle 928. Introducer extension tube 1054 is adapted for passing shaft1052 therethrough, and for being passed within introducer needle 928.Introducer extension tube 1054 may be advanced distally from introducerdistal end 928 a to a site targeted for treatment, e.g., to a selectedlocation within an intervertebral disc. In this way, extension tubedistal end 1054 a (FIG. 61B) may define a starting point for advancementof shaft distal end 1052 a into the disc tissue, and in some embodimentsextension tube distal end 1054 a may define a starting point from whichguiding or steering of shaft distal end 1052 a is initiated. Byselecting a starting point within the disc from which guiding orsteering of shaft distal end 1052 a is initiated, much greater controlcan be exerted over accessing a given target site, and in addition amuch greater range of regions within the disc can be accessed with agiven probe (e.g., with a probe having a shaft of a given length andcurvature).

[0288]FIG. 61B shows shaft distal end 1052 a of the probe of FIG. 61Aextending beyond the distal end of both introducer extension tube 1054and introducer needle 928, with shaft distal end 1052 a adopting acurved configuration. Such a curved configuration allows access to amuch greater number of regions, or to a much larger volume of tissue,within an intervertebral disc, for example, by rotating shaft 1052. Sucha curved configuration may be due to a pre-defined bend or curve inshaft 1052 (e.g., FIGS. 47A-C), or may be the result of a steeringmechanism, the latter well known in the art. In the former situation, apre-defined curvature in shaft 1052 may be restrained or compressedwhile shaft 1052 is within introducer extension tube 1054 or introducerneedle 928. Introducer extension tube 1054 may be rigid or somewhatflexible. Introducer extension tube 1054 may be constructed from anelectrically conductive material such as stainless steel, and the like.Alternatively, introducer extension tube 1054 may be constructed from anelectrically insulating material, such as various plastics, and thelike.

[0289]FIG. 62A shows distal end 1054 a of introducer extension tube 1054advanced to a first position within an intervertebral disc 290. Shaft1052 lies within introducer extension tube 1054, which in turn lieswithin introducer needle 928. Needle distal end 928 a is introducedwithin disc 290, while extension tube distal end 1054 a is advancedslightly distal to needle distal end 928 a. Shaft distal end 1052 aextends beyond extension tube distal end 1054 a and adopts a curvedconfiguration to access a first region, R1, of nucleus pulposus 291.Curvature of shaft distal end 1052 a may result from a predefined biasor curve in shaft 1052, or shaft distal end 1052 a may be steerable.Certain other regions of disc 290 may be accessed by shaft distal end1052 a by circumferentially rotating shaft 1052 about its longitudinalaxis prior to shaft distal end 1052 a being advanced distally beyondextension tube distal end 1054 a (i.e., by rotating shaft 1052 whileshaft 1052 lies within introducer extension tube 1054).

[0290]FIG. 62B schematically represents a situation wherein extensiontube distal end 1054 a is advanced to a second position withinintervertebral disc 290. Much greater control can be exerted over therange of regions within disc 290 that can be accessed by shaft distalend 1052 a when the location of introducer extension tube 1054 isselected prior to advancing shaft distal end 1052 a into the disctissue. For example, as represented in FIG. 62B, by advancing introducerextension tube 1054 distally within introducer needle 928 prior toadvancing shaft distal end 1052 a from introducer extension tube 1054,shaft distal end 1052 a can readily access a second region R2, whereinR2 may be located remote from first region R1 (FIG. 62A). In contrast itis more problematic, if not impossible, for shaft distal end 1052 a toaccess region R2 while introducer extension tube 1054 is positioned inrelation to the disc as shown in FIG. 62A. Similarly, without the use ofintroducer extension tube 1054 (i.e., using an introducer needle 928alone to advance shaft 1052 into the disc) it is problematic, if notimpossible, for shaft distal end 1052 a to access region R2. Theinclusion of an extension device such as introducer extension tube 1054as a component of the instant invention provides major advantages inaccessing a target site within an intervertebral disc or other tissues.

[0291] Although certain embodiments of the invention have been describedprimarily with respect to treatment of intervertebral discs, it is to beunderstood that these methods and apparatus of the invention are alsoapplicable to the treatment of other tissues, organs, and bodilystructures. While the exemplary embodiments of the present inventionhave been described in detail, by way of example and for clarity ofunderstanding, a variety of changes, adaptations, and modifications willbe obvious to those of skill in the art. Therefore, the scope of thepresent invention is limited solely by the appended claims.

What is claimed is:
 1. A method for treating an intervertabral discwithin a patient's spine, the spine comprising a target disc tissue anda non-target tissue, the method comprising: positioning at least oneactive electrode within close proximity of the target disc tissue in thepatient's spine; insulating the non-target tissue from the at least oneactive electrode; and applying a high frequency voltage differencebetween the at least one active electrode and a return electrode, thevoltage difference being sufficient to ablate at least a portion of thetarget disc tissue.
 2. The method of claim 1 further comprisingintroducing a distal end of an electrosurgical instrument through anopening in an annulus fibrosus of the disc, wherein the electrosurgicalinstrument includes a shaft having a shaft distal end portion and ashaft proximal end portion, the shaft distal end portion including anactive side, and the at least one active electrode disposed on theactive side of the electrosurgical probe.
 3. The method of claim 2wherein the shaft distal end portion further includes a non-active sidehaving an insulated external surface, and insulating comprisespositioning the non-active side adjacent to the non-target tissue. 4.The method of claim 3 wherein the non-target tissue comprises the duramater.
 5. The method of claim 2 wherein the shaft comprises a curved orbent distal end.
 6. The method of claim 1 wherein the disc is herniated,the method further comprising: positioning the at least one activeelectrode adjacent an extruded portion of the herniated disc external toan annulus fibrosus; and applying a sufficient high frequency voltagebetween the at least one active electrode and a return electrode toablate at least part of the extruded portion.
 7. The method of claim 1further comprising: introducing the at least one active electrodethrough an opening in an annulus fibrosus of the disc; and applying asufficient high frequency voltage between the at least one activeelectrode and a return electrode to contract collagen fibers of anucleus pulposus.
 8. The method of claim 6 further comprising deliveringan electrically conductive fluid between the at least one activeelectrode and the herniated disc to complete a current flow path betweenthe at least one active electrode and the return electrode.
 9. Themethod of claim 8 further comprising applying a sufficient voltage tothe at least one active electrode in the presence of the electricallyconductive fluid to vaporize at least a portion of the fluid between theat least one active electrode and the herniated disc.
 10. The method ofclaim 9 further comprising accelerating charged particles from thevaporized fluid to the tissue to cause dissociation of the molecularbonds of tissue components within the disc.
 11. The method of claim 8further comprising aspirating at least a portion of the electricallyconductive fluid.
 12. The method of claim 1 wherein the at least oneactive electrode comprises a plurality of active electrodes forming anelectrode array, the method further comprising independently controllingcurrent flow toeach of the active electrodes based on impedance betweenthe active electrodes and the return electrode.
 13. The method of claim1 further comprising positioning the return electrode on the outersurface of the patient's body, and conducting electrical current fromthe active electrode, through the patient's body, to the returnelectrode.
 14. The method of claim 1 wherein the at least one activeelectrode comprises a single, active electrode at the distal end of ashaft.
 15. The method of claim 1 further comprising: aspirating tissuefragments from the disc through an aspiration lumen; and applying a highfrequency voltage to an aspiration electrode coupled to the aspirationlumen, the high frequency voltage being sufficient to remove at least aportion of the tissue fragments.
 16. The method of claim 15 wherein theaspiration electrode comprises a mesh electrode located across a distalopening of the aspiration electrode and having a plurality of openingsfor aspiration of tissue fragments therethrough.
 17. The method of claim15 wherein the aspiration electrode is positioned within the aspirationlumen.
 18. A method of performing spinal surgery, the method comprising:positioning an electrosurgical instrument in close proximity to a spinaldisc, the instrument having an active electrode and a return electrode;applying an electrically conductive fluid toward a distal tip of theelectrosurgical instrument; delivering a high frequency electricalenergy to the active electrode such that the conductive fluid completesa current flow path between the active electrode and the returnelectrode; and aspirating at least a portion of the electricallyconductive fluid through an aspiration lumen, wherein a distal end ofthe aspiration lumen is positioned proximal of the return electrode. 19.The method of claim 18 wherein the distal end of the aspiration lumen isspaced from the spinal disc.
 20. The method of claim 18 furthercomprising: reducing the size of a tissue with an aspiration electrode,wherein the tissue is aspirated through an aspiration lumen.
 21. Themethod of claim 20 wherein reducing comprises ablating the aspiratedtissue within the aspiration lumen.
 22. The method of claim 18 furthercomprising positioning the active electrode and a return electrodewithin the electrically conductive fluid.
 23. The method of claim 18wherein positioning is performed via a percutaneous penetration locatedon the patient's back.
 24. The method of claim 18 further comprisingfusing adjacent vertebrae together after the applying step.
 25. Anelectrosurgical apparatus for treating a target tissue within apatient's spine, the apparatus comprising: a shaft having a shaft distalend portion and a shaft proximal end portion, the shaft distal endportion including an active side and a non-active side, wherein theshaft proximal end portion defines a longitudinal axis of the shaft; atleast one active electrode positioned on the active side of the shaftdistal end portion, an insulator disposed on the non-active side,wherein the insulator is effective in preventing generation of electricfields from the non-active side such that a non-target tissue avoidselectrical damage from the electrosurgical apparatus; a returnelectrode; and a high frequency voltage source for applying a voltagedifference between the at least one active electrode and the returnelectrode, wherein the high frequency voltage is effective in causing atissue altering effect on the target tissue.
 26. The apparatus of claim25 wherein the active electrode extends substantially orthogonal to thelongitudinal axis of the shaft;
 27. The apparatus of claim 25 whereinthe shaft includes a contact surface disposed at the shaft distal endportion, the at least one active electrode comprises an electrode arrayincluding a plurality of electrically isolated active electrodesarranged on the contact surface.
 28. The apparatus of claim 25 whereinthe distal end portion of the shaft is curved or bent.
 29. The apparatusof claim 25 wherein the insulator is positioned substantially oppositethe active electrode, and the insulator is effective in preventingelectrical damage to a dura mater of the spine.
 30. The apparatus ofclaim 25 further comprising a fluid delivery element for delivering anelectrically conductive fluid to the shaft distal end portion, theelectrically conductive fluid providing a current flow path between theactive electrode and the return electrode.
 31. The apparatus of claim 30wherein the fluid delivery element comprises a fluid delivery tubeintegral with the shaft, the fluid delivery tube having an outletlocated distal to the return electrode, and the return electrode isspaced proximal to the active electrode.
 32. The apparatus of claim 25wherein the active electrode comprises a single active electrode. 33.The apparatus of claim 25 further comprising a fluid aspiration elementfor aspirating fluid from the target site, the fluid aspiration elementincluding a suction inlet and a suction lumen, the suction inlet locatedon the shaft at a location proximal to the return electrode.
 34. Theapparatus of claim 33 further comprising an aspiration electrode forablating tissue fragments which contact the aspiration electrode,wherein the aspiration electrode is arranged adjacent or within thefluid aspiration element.
 35. The apparatus of claim 33 furthercomprising an aspiration electrode disposed within the fluid aspirationelement for ablating tissue fragments aspirated into the fluidaspiration element.
 36. The apparatus of claim 25 wherein the tissuealtering effect is selected from the group consisting of: a decrease involume of the target tissue by molecular dissociation of tissuecomponents, and contraction of collagen fibers of the target tissue. 37.The apparatus of claim 25 further comprising an electrically insulatingsupport member extending from the distal end-portion of the shaft, theat least one active electrode mounted on the support member.
 38. Anapparatus for performing spinal surgery, the apparatus comprising: ashaft defining a distal end portion; at least one active electrodepositioned on the distal end portion of the shaft; a return electrodepositioned proximal of the active electrode; a fluid delivery lumen thatdelivers a conductive fluid to a point distal to the return electrode; ahigh frequency energy source configured to create a voltage differencebetween the active electrode and the return electrode; and an aspirationlumen comprising an opening positioned proximal of the return electrode,wherein the aspiration lumen is configured to aspirate the conductivefluid over the return electrode so as to complete a current flow pathbetween the active electrode and the return electrode.
 39. The apparatusof claim 38 wherein at least one of the fluid delivery lumen and theaspiration lumen has a cross-sectional shape which is at least partlyannular.
 40. A method of treating an intervertebral disc having anucleus pulposus and an annulus fibrosus, the method comprising:advancing a distal end of an electrosurgical instrument into the annulusfibrosus, wherein an active electrode and a return electrode arepositioned on the distal end of the electrosurgical instrument; movingthe distal end of the electrosurgical instrument to a curvedconfiguration that approximates a curvature of an inner surface of theannulus fibrosus; and delivering a high frequency voltage between theactive electrode and the return electrode to treat the inner surface ofthe annulus fibrosus.
 41. The method of claim 40, wherein advancingcomprises channeling through the annulus fibrosus by delivering a highfrequency voltage between the active electrode and the return electrode.42. The method of claim 40 wherein moving comprises biasing the distalend.
 43. The method of claim 40 wherein moving comprises steering thedistal end.
 44. The method of claim 43 wherein steering comprisesactuating an actuator positioned at the proximal portion of theelectrosurgical instrument.
 45. The method of claim 40 furthercomprising tracking the movement or location of the distal end of theelectrosurgical instrument.
 46. The method of claim 45 wherein trackingcomprises visualizing the distal end fluoroscopically.
 47. The method ofclaim 40 wherein advancing comprises positioning the active electrodeand return electrode within the nucleus pulposus.
 48. A method oftreating an intervertebral disc, the method comprising: positioning adistal end of an electrosurgical probe within close proximity of anouter surface of the intervertebral disc, the distal end of theelectrosurgical probe comprising at least one active electrode;delivering a high frequency voltage between the at least one activeelectrode and a return electrode, the high frequency voltage beingsufficient to create a channel in the disc tissue; advancing the activeelectrode through the channel created in the intervertebral disc;conforming the distal end of the electrosurgical probe to a curvedconfiguration that approximates a curvature of an inner surface of anannulus fibrosus; and delivering a high frequency voltage between theactive electrode and the return electrode to treat the inner surface ofthe annulus fibrosus.
 49. The method of claim 48 further comprisingdelivering a heating voltage between a coagulation electrode and thereturn electrode to heat at least a portion of the intervertebral disc,wherein the heating voltage is sufficient to coagulate a severed bloodvessel, and the heating voltage is insufficient to induce moleculardissociation of disc tissue components ablate the intervertebral disctissue.
 50. The method of claim 48 wherein conforming comprises biasingthe distal end or steering the distal end.
 51. An apparatus for treatingintervertebral discs, the apparatus comprising: a steerable shaftdefining a shaft distal end portion, wherein the shaft distal endportion is moveable to a curved configuration that approximates thecurvature of the inner surface of an annulus fibrosus; at least oneactive electrode positioned on the distal end portion of the shaft; areturn electrode positioned proximal of the at least one activeelectrode; and a high frequency energy source configured to create avoltage difference between the active electrode and the returnelectrode.
 52. The apparatus of claim 51 further comprising a fluiddelivery lumen configured to deliver a conductive fluid to the at leastone active electrode.
 53. The apparatus of claim 51 further comprisingan aspiration lumen adapted to aspirate the conductive fluid to alocation adjacent the active electrode.
 54. The apparatus of claim 51,further comprising a coagulation electrode coupled to the high frequencyenergy source.
 55. The apparatus of claim 51, wherein the high frequencyvoltage source is configured to deliver a high frequency voltage to thecoagulation electrode, wherein the high frequency voltage isinsufficient for the coagulation electrode to produce an effect selectedfrom the group consisting of: generating a plasma in the presence of anelectrically conductive fluid, ablating tissue in a temperature range of45° to 90° C., and causing molecular dissociation of tissue components56. A method of using an electrosurgical system for alleviation ofspinal pain by targeted electrosurgery of an intervertebral disc of apatient, the electrosurgical system including a power supply unitfunctionally coupled to at least one active electrode, the at least oneactive electrode disposed on a shaft distal end of an electrosurgicalinstrument, and the method comprising: a) advancing an introducer needletowards the intervertebral disc, the introducer needle including a lumenand a needle distal end; and b) passing the shaft distal end through thelumen distally beyond the needle distal end, wherein the shaft distalend avoids contact with the needle distal end.
 57. The method of claim56, further comprising: c) guiding the shaft distal end within theintervertebral disc such that the at least one active electrode contactsat least a first region of disc tissue; and d) applying a high frequencyvoltage between the at least one active electrode and at least onereturn electrode, wherein tissue components of at least a portion of thefirst region of disc tissue are ablated.
 58. The method of claim 57,further comprising: e) retracting the shaft distal end into the lumen ofthe introducer needle, wherein the shaft distal end avoids contact withthe needle distal end.
 59. The method of claim 57, wherein during saidstep b) the at least one active electrode avoids contact with the needledistal end.
 60. The method of claim 57, wherein said step d) results inmolecular dissociation of tissue components of the first region, and thevolume of the nucleus pulposus is decreased.
 61. The method of claim 57,wherein the guiding step is performed after the shaft distal end hasbeen extended distally beyond the needle distal end.
 62. The method ofclaim 57, wherein the guiding step is performed before the shaft distalend has been extended distally beyond the needle distal end the guidingstep comprises rotating the shaft about its longitudinal axis.
 63. Themethod of claim 57, wherein the guiding step comprises: axiallytranslating the shaft within the lumen of the introducer needle; androtating the shaft about its longitudinal axis.
 64. The method of claim57, wherein the shaft has a pre-defined curvature both prior to andafter said guiding step.
 65. The method of claim 57, wherein the shafthas a linear configuration prior to said guiding step, and said guidingstep comprises conforming the shaft into a non-linear configuration. 66.The method of claim 65, wherein the guiding step comprises steering theshaft distal end by application of a lateral force to the shaft.
 67. Themethod of claim 56, wherein the method is performed percutaneously. 68.The method of claim 57, wherein the first region of disc tissuecomprises a target site, said step c) is performed under fluoroscopy,and the position of the shaft distal end relative to the target site isvisualized fluoroscopically.
 69. The method of claim 68, wherein theshaft includes a radiopaque tracking device on the shaft distal end, orat least one radiopaque depth marking.
 70. The method of claim 64,wherein the pre-defined curvature results from at least one curve in adistal portion of the shaft.
 71. The method of claim 70, wherein the atleast one curve comprises a first curve and a second curve proximal tothe first curve, and the first curve and the second curve are in thesame plane relative to the longitudinal axis of the shaft, and the firstcurve and the second curve are in opposite directions.
 72. The method ofclaim 71, wherein the shaft distal end comprises a first curve and asecond curve proximal to the first curve, the first curve ischaracterized by a first angle and the second curve is characterized bya second angle, wherein the first angle determines a transverse locationof the shaft distal end within the lumen of the introducer needle, andthe second angle determines an amount of deflection of the shaft distalend away from the longitudinal axis of the shaft proximal end.
 73. Themethod of claim 57, wherein the at least one return electrode is locatedon the shaft or on a dispersive pad.
 74. The method of claim 57, whereinthe at least one active electrode comprises an electrode head having asubstantially apical spike and a substantially equatorial cusp, and theapical spike and the equatorial cusp provide a high current density inthe vicinity of the electrode head upon application of the highfrequency voltage between the at least one active electrode and thereturn electrode, the high current density promotes formation of aplasma in the vicinity of the electrode head, and the plasma causeslocalized ablation of disc tissue at a temperature in the range of fromabout 45° C. to about 90° C.
 75. The method of claim 57, wherein theintervertebral disc includes a fragment of nucleus pulposus within anannulus fibrosus, and the shaft distal end portion is guided such thatthe at least one active electrode is in the vicinity of the fragment ofthe nucleus pulposus.
 76. The method of claim 57, wherein theintervertebral disc includes an annulus fibrosus having at least oneannular fissure therein, and the shaft distal end portion is guided suchthat the at least one active electrode is in the vicinity of the atleast one annular fissure.
 77. The method of claim 57, wherein theintervertebral disc includes a bulge in the nucleus pulposus, and theshaft distal end portion is guided such that the at least one activeelectrode is in the vicinity of the bulge.
 78. The method of claim 57,wherein the method is performed in conjunction with epidural injectionof a steroid.
 79. The method of claim 57, further comprising the stepof: f) introducing an ancillary device into the disc, wherein theancillary device is selected from the group consisting of an endoscope,an aspiration device, a return electrode, and a fluid delivery device.80. A method of ablating tissue at a target site of an intervertebraldisc, comprising: a) providing an electrosurgical system including ainstrument, an introducer needle, and a power supply unit coupled to theinstrument, the instrument having a shaft, the shaft including a distalend portion having at least one active electrode, the introducer needlehaving a lumen for accommodating axial movement of the shaft therein; b)advancing the introducer needle towards the intervertebral disc; c)passing the shaft distal end portion distally through the lumen of theintroducer needle towards the disc, wherein the shaft distal end portionis inserted within the disc; d) guiding the shaft distal end portion tothe target site within the disc; and e) applying a high frequencyvoltage between the at least one active electrode and at least onereturn electrode, the high frequency voltage selected for ablating disctissue at the target site.
 81. The method of claim 80, wherein the shaftdistal end portion has a pre-defined curvature, and said step d)comprises: f) during said step c), rotating the shaft about itslongitudinal axis.
 82. The method of claim 80, wherein the method isperformed percutaneously under fluoroscopy, and the position of theshaft distal end portion relative to the target site is visualizedfluoroscopically.
 83. The method of claim 80, wherein said step e)results in ablation of disc tissue, the volume or the mass of the disctissue is decreased, and discogenic pain is alleviated.
 84. The methodof claim 80, wherein said step e) comprises applying a high frequencyvoltage in the range of from about 150 volts rms to about 350 volts rmsbetween the at least one active electrode and the at least one returnelectrode, such that disc tissue at the target site is ablated at atemperature in the range of from about 45° C. to about 90° C.
 85. Themethod of claim 80, further comprising: g) after said step e),contacting tissue within the disc with the shaft distal end portion, andthereafter repeating said step e).
 86. The method of claim 80, furthercomprising: h) applying a quantity of an electrically conductive fluidin the vicinity of the at least one active electrode.
 87. The method ofclaim 80, wherein the introducer needle includes a needle distal end,and said step b) comprises: i) advancing the introducer needle through afirst wall of the annulus fibrosus until the needle distal end contactsthe nucleus pulposus; and said step d) comprises: j) advancing the shaftdistal end portion distally from the needle distal end until the atleast one active electrode contacts an opposite wall of the annulusfibrosus; and k) after said step j), retracting the shaft proximally adefined distance.
 88. The method of claim 80, wherein the shaft includesa first curve and a second curve proximal to the first curve, and thefirst curve and the second curve are in the same plane relative to thelongitudinal axis of the shaft, and the first curve and the second curveare in opposite directions.
 89. The method of claim 80, wherein the atleast one active electrode includes a filament, the shaft includes afirst insulating sleeve encasing the filament, a return electrode on thefirst insulating sleeve, an insulating collar located at a distal end ofthe first insulating sleeve proximal to the return electrode, a secondinsulating sleeve on the return electrode, and a shield on the secondinsulating sleeve.
 90. The method of claim 80, wherein the at least oneactive electrode comprises an electrode head having a substantiallyapical spike and a substantially equatorial cusp, and the apical spikeand the equatorial cusp provide a high current density in the vicinityof the electrode head upon execution of said step e).
 91. The method ofclaim 80, wherein the target site includes a disc defect selected fromthe group consisting of: a fragmented nucleus pulposus, a bulge in thenucleus pulposus, and an annular fissure.
 92. The method of claim 80,further comprising the step of: l) injecting a steroid into an epiduralspace adjacent to the intervertebral disc.
 93. The method of claim 80,further comprising the step of: m) changing the location of the needledistal end relative to the intervertebral disc to define an appropriateposition within the intervertebral disc from which the shaft distal endportion is guided in said step d).
 94. The method of claim 80, whereinthe electrosurgical system further includes an introducer extension tubehaving a distal end, and the method further comprises the step of: n)advancing or retracting the introducer extension tube distal end to aselected location within the intervertebral disc.
 95. The method ofclaim 94, wherein said step n) comprises advancing or retracting theintroducer extension tube within the lumen of the introducer needle, andsaid step d) comprises guiding the shaft distal end portion from theintroducer extension tube distal end.
 96. A method of targeted treatmentof an intervertebral disc, comprising: guiding a shaft of anelectrosurgical probe to a target site of the disc, the shaft having anactive electrode disposed on a shaft distal end; and applying a highfrequency voltage between the active electrode and a return electrode,wherein disc tissue at the target site is ablated at a temperature inthe range of from about 45° C. to about 90° C., wherein the shaftassumes a linear configuration in the absence of an applied force, andthe shaft is steerable by adoption of a non-linear configuration in thepresence of an applied force.
 97. The method of claim 96, furthercomprising the steps of: introducing a distal end of an introducerneedle into an intervertebral disc, the introducer needle having a lumentherethrough; and advancing an introducer extension tube through thelumen of the introducer needle such that a distal end of the introducerextension tube is positioned at a selected location within theintervertebral disc, and wherein said guiding comprises steering theshaft distal end from the selected location within the intervertebraldisc.
 98. An electrosurgical probe and introducer needle combination fortreating an intervertebral disc, comprising: a probe including a shaft,the shaft including a shaft distal end and at least one activeelectrode; an introducer extension tube having an extension tube distalend, the introducer extension tube adapted for passing the shaft distalend therethrough; and an introducer needle having a lumen and a needledistal end, the introducer needle adapted for advancing and retractingthe introducer extension tube within the lumen of the introducer needleand for advancing the introducer extension tube distally beyond theneedle distal end.
 99. The combination of claim 98, wherein the shaftdistal end is curved or steerable.
 100. The combination of claim 98,wherein the shaft distal end has a first curve in a first direction anda second curve proximal to the first curve, the second curve in adirection opposite the first direction.
 101. A method of advancing andretracting a medical instrument through an introducer device, comprisingthe steps of: a) advancing a distal end of the medical instrumentdistally beyond a distal end of the introducer device, wherein thedistal end of the medical instrument does not contact the distal end ofthe introducer device, and wherein the distal end of the medicalinstrument includes a first curve and a second curve proximal to thefirst curve, the first curve is in a first direction and the secondcurve is in a second direction opposite to the first direction; and b)retracting the distal end of the medical instrument into the distal endof the introducer device, wherein the distal end of the medicalinstrument does not contact the distal end of the introducer device.102. The method of claim 101, wherein said step a) comprises passing themedical instrument within a lumen of the introducer device, and thedistal end of the medical instrument occupies a substantially centraltransverse location within the lumen of the introducer device.
 103. Themethod of claim 101, wherein the introducer device is selected from thegroup consisting of: an introducer needle, an introducer extension tube,a catheter, a cannula, an endoscope, and a hypodermic needle.
 104. Themethod of claim 101, wherein the medical instrument is selected from thegroup consisting of: an electrosurgical probe, an endoscope, a trocar,and a fluid delivery device.